nu = constantMedir es comparar una magnitud desconocida con la e un patrón que tomamos como referencia y cuyo valor llamamos unidad. El resultado de la medida es el producto de un número real por la unidad de referencia.
Hay unidades fundamentales que se eligen arbitrariamente y derivadas que se definen a partir de las fundamentales.
El sistema internacional de unidades (SI) se elabora por la Conferencia General de Pesas y Medidas, que se reune para corregirlo cada cuatro años.
El SI consta de 7 unidades fundamentales, las unidades 2 suplementarias y las unidades derivadas.
Para cada magnitud se define una unidad a la que se le asigna un símbolo. El nombre de la unidad se escribe con minúscula y, si es necesario, en plural (por ejemplo 10 newtons, 3 vatios). El símbolo generalmente se escribe con caracteres romanos y en minúsculas, excepto si deriva de un nombre propio, en cuyo caso suele hacerse con mayúscula (por ejemplo 10 N, 3 W). Hay alguna excepción como el ohmio (que puede escribirse con la letra griega omega mayúscula 5 ohmios = 5 ohm = 5 Ω). El símbolo no van seguidos de punto ni toman la s del plural. Con los símbolos se usan prefijos de múltiplos y submúltiplos que van unidos, sin espacios el símbolo. Los exponentes de un símbolo afectan también al prefijo: = 1000000 m2 = 1 (km)2 = 1 km2 ≠ 1 k(m)2 = 1000 m2
| Magnitud | Unidad | Símbolo | Definición |
| Longitud | metro | m | Distancia recorrida en el vacío por la luz en 1/299792458 segundos |
| Masa | kilogramo | kg | Masa del patrón de platino iridiado depositado en el Museo Internacional de Pesas y Medidas |
| Tiempo | segundo | s | Duración de 9 192 631 770 periodos de la radiación hiperfina del Cesio 133 |
| Intensidad de corriente eléctria | amperio | A | Corriente que produce una fuerza de 2 x 107 por metro entre dos conductores situados a 1 m en el vacío. |
| Temperatura termodinámica | kelvin | K | (1/273'16) de la temperatura del punto triple del agua |
| Cantidad de materia | mol | mol | Número de átomos de carbono 12 cuya masa conjunta hace 0'012 kg |
| Intensidad luminosa | candela | cd | Intensidad luminosa producida por una radiación monocromática de 540 x 1012 Hz cuya intensidad energética es 1/683 W/sr |
| Magnitud | Unidad | Símbolo | Tipo | Definición |
| Ángulo plano | radián | rad | adimensional | 1/(2π) veces el ángulo de una circunferencia |
| Ángulo sólido | estereoradián | sr | adimensional | 1/(4π) veces el ángulo sólido de una esfera |
| Magnitud | Unidad | Tipo | Equivalencia habitual | Equivalencia fundamental |
| Superficie | metro cuadrado | mecánica geométrica | m2 | m2 |
| Volumen, capacidad | metro cúbico | mecánica geométrica | m3 | m3 |
| Velocidad lineal | metros por segundo | mecánica cinemática | m/s | m•s-1 |
| Aceleración lineal | metros por segundo al cuadrado | mecánica cinemática | m/s2 | m•s-2 |
| Velocidad angular | radianes por segundo | mecánica cinemática | rad/s | rad•s-1 |
| Aceleración angular | radianes por segundo al cuadrado | mecánica cinemática | rad/s2 | rad•s-2 |
| Capacidad térmica, entropía | julio por kelvin kelvin | calor | J/K | m2•kg•s-2•K-1 |
| Capacidad calorífica específica | julio por kilogramo y kelvin | calor | J/(kg•K) | m2•s-2•K-1 |
| Conductividad calorífica | vatio por metro y kelvin | calor | W/(m•K) | m•kg•s-3•K-1 |
| Caudal volumétrico | metro cúbico por segundo | caudal | m3/s | m3•s-1 |
| Caudal másico | kilogramo por segundo | caudal | kg/s | kg•s-1 |
| Densidad de masa lineal | kilogramo por metro (=10^6 tex) | caudal | kg/m | m-1•kg |
| Densidad de masa volumétrica | kilogramo por metro cúbico | caudal | kg/m3 | m-3•kg |
| Viscosidad dinámica | pascal segundo = 10 poises | caudal | Pa•s | m-1•kg•s-1 |
| Viscosidad cinemática | m2/s = 10^4 stokes | caudal | m2/s | m2•s-1 |
| Campo eléctrico | voltio por metro | electromagnetismo | V/m | m•kg•s-3•A-1 |
| Magnitud | Unidad | Símbolo | Tipo | Equivalencia habitual | Equivalencia fundamental |
| Frecuencia | hercio | Hz | tiempo | s-1 | |
| Fuerza | newton | N | mecánica dinámica | m•kg•s-2 | |
| Presión, tensión | pascal | Pa | mecánica dinámica | N/m2 | m-1•kg•s-2 |
| Energía, trabajo, cantidad de calor | julio | J | mecánica dinámica | N•m | m2•kg•s-2 |
| Potencia, flujo radiante | vatio | W | mecánica dinámica | J/s | m2•kg•s-3 |
| Cantidad de electricidad, carga eléctrica | culombio | C | electromagnetismo | A•s | |
| Potencial eléctrico, fuerza electromotriz | voltio | V | electromagnetismo | m2•kg•s-3•A-1 | |
| Resistencia eléctrica | omhio | ohm, Ω | electromagnetismo | V/A | m2•kg•s-3•A-2 |
| Conductancia eléctrica | siemens | mho, S, Ω-1 | electromagnetismo | A/V | m-2•kg-1•s3•A2 |
| Capacidad eléctrica | faradio | F | electromagnetismo | C/V | m-2•kg-1•s4•A2 |
| Flujo magnético, flujo de inducción magnética | weberio | Wb | electromagnetismo | V•s | m2•kg•s-2•A-1 |
| Densidad de flujo magnético, inducción magnética | tesla | T | electromagnetismo | Wb/m2 | kg•s-2•A-1 |
| Inductancia | henrio | H | electromagnetismo | Wb/A | m2•kg•s-2•A-2 |
| Flujo luminoso | lumen | lm | cd•sr | ||
| Iluminancia | lux | lx | lm/m2 | m-2•cd•sr | |
| Actividad de un radionucleido | becquerelio | Bq | s-1 | ||
| Dosis absorbida | gray | Gy | J/kg | m2•s-2 | |
| Dosis equivalente | sievert | Sv | J/kg | m2•s-2 |
| Magnitud | Unidad | Símbolo | Tipo | Definición |
| Diferencia de nivel entre dos señales periódicas | decibelio | dB | adimensional | 10 lg (P1/P2) = 20 lg (A1/A2) |
| Diferencia de nivel entre dos señales periódicas | neperio | Np | adimensional | ln (A1/A2) = 1/2 ln (P1/P2) |
| Índice de refracción | n | adimensional |
n = c0/c c0 velocidd
en el vacío |
|
| Condición de un flujo | número de Reynolds | R | adimensional |
R = ρvD/μ ρ densidad |
A unit of a quantity is the standard quantity used to measure a physical quantity.
The process of measuring a physical quantity has two steps:
In order to measure the length of a table, the unit selected is that of length. If metre is the unit used, a metre rod is used to measure the length and if the table length is thrice the length of the metre rod, then the numerical value of length of the table is 3.
i.e., Table length = 3 x 1m = 3m
In general, measure of a physical quantity = numerical value of physical quantity x size of its unit
i.e., x = nu
where x = quantity to be measured for selected unit
n = numerical value of physical quantity
u = size of the unit
If size of the chosen unit is small, then numerical value is large and vice versa. But measure of physical quantity is always the same.
nu = constant
If n1 and n2 are numerical values of physical quantities for units u1 and u2, then,
n1 u1 = n2 u2.
Physical quantities and units follow the same hierarchy; chosen base quantities have defined base units, from these any other quantities may be derived and have corresponding derived units.
Most physical quantities include a unit, but not all - some are dimensionless. Neither the name of a physical quantity, nor the symbol used to denote it, implies a particular choice of unit, though SI units are usually preferred and assumed today due to their ease of use and all-round applicability.
For example, a quantity of mass might be represented by the symbol m, and could be expressed in the units kilograms (kg), pounds (lb), or Daltons (Da).
The characteristics of several chosen units are:
Before all the branches of science were clubbed together under the nomenclature 'Natural philosophy', under which all observations of subjective nature were being carried out and spirit of enquiry was almost non-existent, we were satisfied with simple explanations.
The subjective interpretation including measurement, obviously varies from person to person, since the interpretation is based on one's senses. Gradually, the generations began to ask 'how' things are happening. Thus, the observations became more objective. Thus, physics - one of the many sciences, became a subject of observation and measurement.
When we quantify, what we are observing, then such an observation is a science or knowledge. However, without the quantification of an observation, thought is simply a process of gaining knowledge, but has yet to reach a stage, to be called a 'science'.
Hence, to call a subject 'science', the thought process ultimately has to be quantified suitably, using appropriate units of measurement.
There are 7 physical quantities viz., Length, mass, time, temperature, electric current, luminous intensity and amount of substance.
Length, mass and time are called fundamental physical quantities.
The units of fundamental physical quantities are called fundamental units. They are m, kg and sec. These units can neither be derived from one another nor can be resolved into other units. They are independent to each other.
Units of physical quantities can be expressed in terms of fundamental units and such units are called derived units.
Unit of area can be an example for derived unit. If L is the length of square then L x L = L2 is its area. Similarly, the volume of a cube is L x L x L = L3 cubic area. Units of any physical quantity can be derived from its defining equation.
The characteristics of several chosen units are:
Following are the common system of units to measure mass, length and time.
Fundamental units of length, mass and time are centimetre, gram and second.
Fundamental units of length, mass and time are metre, kilogram and second. It is a coherent system of units in mechanics.
Known as British system of units, it is not a metric system. It stands for foot, pound and second. Its use is declining in scientific work.
It is a new system introduced by General Conference of Weights and Measures in 1960. It is called "Le Systeme International d' Unites".
| Basic physical quantity | Unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | Second | s |
| Temperature | kelvin | K |
| Electric current | ampere | A |
| Luminous intensity | candela | cd |
| Quantity of matter | mole | mol |
Supplementary quantities and their units
| Physical quantity | Unit | Symbol |
|---|---|---|
| Plane angle | radian | rad |
| Solid angle | Steradian | sr |
| Radioactivity | Curie | ci |
Prefixes are used for large and small quantities. The following table gives prefixes, their symbol and their values in powers of 10, as used in SI units.
| Prefix | Symbol | Power of 10 |
|---|---|---|
| deci | d | 10 - 1 |
| deka | da(D) | 10 1 |
| centi | c | 10 - 2 |
| hecto | h | 10 2 |
| milli | m | 10 - 3 |
| kilo | k | 10 3 |
| micro | μ | 10 - 6 |
| mega | M | 10 6 |
| nano | n | 10 - 9 |
| giga | G | 10 9 |
| pico | P | 10 - 12 |
| tera | T | 10 12 |
| femto | f | 10 - 15 |
| peta | P | 10 15 |
| atto | a | 10 - 18 |
| exa | E | 10 18 |
| zepta | z | 10 - 21 |
| zetta | Z | 10 21 |
| yocto | y | 10 - 24 |
| (yotto) | Y | 10 24 |
Among the systems of units mentioned above, the SI units i.e., Le systeme internationale d' unites, is a new, comprehensive and rationalised system of units, accepted by the 11th conference of weights and measures in 1960. It is used in science and technology all over the world, because of the following advantages over others.
However, the SI units are governed by the following rules:
E.g., newton and not Newton.
E.g., J for joule, K for Kelvin.
E.g., 5 kg (not 5 kgs), 25 m (not 25 metres).
E.g., Nm and not N m or N x m.
E.g., 0.7kg & not .7kg
E.g., 16 mm film. For writing the thickness of a glass of 10 mm, it is written as 10 mm and not 10-mm.
E.g., 6 kg and not 6kg
The shortest distance between the two ends of a body is its length. During 1120 A.D., the King of England had enforced the usage of 'Yard' in his country, as the unit of length, which was equal to the distance from the tip of his nose to the end of his out stretched arm. Similarly, the King of France had declared the length of the Royal foot of the King as a measure and called it one foot. But in 1799, the foot was replaced by 'metre', equal to one-tenmillionth the distance of the equator to the north pole along a longitudinal line that passes through Paris.
In 1889, 1 metre was defined as the distance between 2 lines on a specific platinum-iridium bar stored under controlled conditions near Paris. Since the S and T demanded more precise standard, in 1960, 1 metre was redefined as 1, 650, 763.73 wavelengths of a particular orange-red light emitted by atoms of krypton-86 in a gas discharge tube. But of late, 1 metre is defined as the length of the path travelled by light in vacuum during a time interval of 1/299, 792, 458 of a second. This unit is believed to be absolutely constant.
Distance travelled by light in a time interval of one planck time, the shortest distance possible, is 10-43 m.
One fermi = 10-15 m used to measure nuclear dimensions.
One angstrom = 10-10 m used to measure atomic dimensions.
It is used in measuring long distances converted with solar studies in astronomy.
1 Au = 1.496 x 1011m, the mean distance between the sun and the Earth.
is the distance travelled by light in vacuum in one year.
Distance = velocity x time
One light year = 3 x 108 m/s x 1
= 3 x 108 x 365 x 24 x 60 x 60 x m/s x s
= 9.46 x 1015 m
This unit is used to measure intergalactic distances as well as stellar distances.
The distance at which the mean radius of the Earth's orbit subtends an angle of one second of arc.
The metric system is an international decimalised system of measurement.
The main feature of the metric system is the standard set of inter-related base units and a standard set of prefixes in powers of ten. These base units are used to derive larger and smaller units and replace a huge number of unstandardised units of measure that existed previously. While the system was first developed for commercial use, its coherent set of units made it particularly suitable for scientific and engineering purposes.
The metric system is decimal. All multiples and divisions of the base units are factors of the power of ten. An prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol. At present there are specified twenty prefixes.
The long and short scales are two of several different large-number naming systems used throughout the world for integer powers of ten. Many countries, including most in continental Europe, use the long scale whereas most English-speaking countries use the short scale.
| Prefix | Symbol | 10n | Decimal |
Long scale (Europe) |
Short scale (US) |
| yotta | Y | 1024 | 1000000000000000000000000 | Quadrillion | Septillion |
| zetta | Z | 1021 | 1000000000000000000000 | Trilliard | Sextillion |
| exa | E | 1018 | 1000000000000000000 | Trillion | Quintillion |
| peta | P | 1015 | 1000000000000000 | Billiard | Quadrillion |
| tera | T | 1012 | 1000000000000 | Billion | Trillion |
| giga | G | 109 | 1000000000 | Milliard | Billion |
| mega | M | 106 | 1000000 | Million | |
| kilo | k | 103 | 1000 | Thousand | |
| hecto | h | 102 | 100 | Hundred | |
| deca | da (D) | 101 | 10 | Ten | |
| 100 | 1 | One | |||
| deci | d | 10-1 | 0.1 | Tenth | |
| centi | c | 10-2 | 0.01 | Hundredth | |
| milli | m | 10-3 | 0.001 | Thousandth | |
| micro | μ | 10-6 | 0.000001 | Millionth | |
| nano | n | 10-9 | 0.000000001 | Milliardth | Billionth |
| pico | p | 10-12 | 0.000000000001 | Billionth | Trillionth |
| femto | f | 10-15 | 0.000000000000001 | Billiardth | Quadrillionth |
| atto | a | 10-18 | 0.000000000000000001 | Trillionth | Quintillionth |
| zepto | z | 10-21 | 0.000000000000000000001 | Trilliardth | Sextillionth |
| yocto | y | 10-24 | 0.000000000000000000000001 | Quadrillionth | Septillionth |
The uncoordinated use of the metric system by different scientific and engineering disciplines, particularly in the late nineteenth century, resulted in different choices of fundamental units, even though all were based on the same definitions of the metre and the kilogram. During the twentieth century, efforts were made to rationalise these units and in 1960 the CGPM published the International System of Units ("Système international d'unités" in French, hence "SI") which, since then, has been the internationally recognised standard metric system, though the cgs system is also in use.
The centimetre gram second system of units (cgs or CGS) was the first coherent metric system, having been developed in the 1860s and promoted by Maxwell and Thomson. The cgs system is a metric system of physical units based on centimetre as the unit of length, gram as a unit of mass, and second as a unit of time. All CGS mechanical units are unambiguously derived from these three base units, but there are several different ways of extending the CGS system to cover electromagnetism.
Density is expressed in g/cm3, force expressed in dynes and mechanical energy in ergs. Thermal energy was defined in calories, one calorie being the energy required to raise the temperature of one gram of water from 15.5 °C to 16.5 °C. It was proposed two sets of units for electrical and magnetic properties - the electrostatic set of units and the electromagnetic set of units.
| Quantity | Symbol | CGS unit | CGS unit abbreviation |
Definition | Equivalent in SI units |
|---|---|---|---|---|---|
| length, position | L, x | centimetre | cm | 1/100 of metre | = 10−2 m |
| mass | m | gram | g | 1/1000 of kilogram | = 10−3 kg |
| time | t | second | s | 1 second | = 1 s |
| velocity | v | centimetre per second | cm/s | cm/s | = 10−2 m/s |
| acceleration | a | gal | Gal | cm / s2 | = 10−2 m/s2 |
| force | F | dyne | dyn | g cm / s2 | = 10−5 N |
| energy | E | erg | erg | g cm2 / s2 | = 10−7 J |
| power | P | erg per second | erg/s | g cm2 / s3 | = 10−7 W |
| pressure | p | barye | Ba | g / (cm s2) | = 10−1 Pa |
| dynamic viscosity | μ | poise | P | g / (cm s) | = 10−1 Pa·s |
| wavenumber | k | kayser | cm−1 | cm−1 | = 100 m−1 |
The MKS system of units is a physical system of units that expresses any given measurement using fundamental units of the metre, kilogram, and/or second.
The cgs units of electricity were cumbersome to work with. This was remedied at the 1893 International Electrical Congress held in Chicago by defining the "international" ampere and ohm using definitions based on the metre, kilogram and second. In 1901, Giorgi showed that by adding an electrical unit as a fourth base unit, the various anomalies in electromagnetic systems could be resolved. The metre-kilogram-second-coulomb (MKSC) and metre-kilogram-second-ampere (MKSA) systems are examples of such systems.
The metre-tonne-second system of units (MTS) was based on the metre, tonne and second - the unit of force is the sthène and the unit of pressure is the pièze. It was invented in France in industry and was mostly used in the Soviet Union from 1933 to 1955.
Gravitational metric systems use the kilogram-force (kilopond) as a base unit of force, with mass measured in a unit known as the hyl, TME, mug or metric slug. Note these are not part of the International System of Units (SI).
In 1960, the Eleventh General Conference of Weights and Measures recommended an International System of Units (abbreviated as SI) based on the metric system of measurement. When the recommendation was accepted in 1968, it marked the first time in world history that a single system of units had been established internationally. The International System of Units (System international units or SI) is the current international standard metric system and the system most widely used around the world in many fields of commerce, science and engineering. However, there still remain certain subfields where CGS is prevalent. The SI is an extension of Giorgi's MKSA system; It is devised around seven base units which are the metre, kilogram, second, ampere, kelvin, candela and mole.
The system has been nearly globally adopted with the United States being the only industrialized nation that does not mainly use the metric system in its commercial and standards activities. The United Kingdom has officially adopted metrication, but not with the intention of replacing customary measures entirely. Canada has adopted it for all legal purposes but imperial/US units are still in use, particularly in the buildings trade.
In this system the units are based on specific quantities, which do not vary. You will notice that the quantities do not vary and are independent of different environmental factors. For example, in this system:
The units are divided into two classes: base units and derived units. There are seven base units, each representing, by convention, different kinds of physical quantities.
The units of fundamental physical quantities are called fundamental or base units. These units can neither be derived from one another nor can be resolved into any other units. They are independent of one another.
| Name | Unit symbol | Quantity | Typical Symbol for Variables |
|---|---|---|---|
| metre | m | length | l (a lowercase L) |
| kilogram [1] | kg | mass | m |
| second | s | time | t |
| ampere | A | electric current | I (a capital i) |
| kelvin | K | thermodynamic temperature | T |
| candela | cd | luminous intensity | Iv (a capital i with lowercase non-italicized v subscript) |
| mole | mol | amount of substance | n |
| Note [1]: Despite the prefix, the kilogram is the base unit of mass. The kilogram, not the gram, is used in the definitions of derived units. | |||
Units of physical quantities that can be expressed in terms of fundamental units are called derived units. Unit of area can be an example for derived unit. If L is the length of square then L x L = L2 is its area. Units of any physical quantity can be derived from its defining equation.
Derived units are formed from multiplication and division of the seven base units and other derived units and are unlimited in number; for example, the SI derived unit of speed is metre per second, m/s. Some derived units have special names; for example, the unit of resistance, the ohm, symbol Ω, is uniquely defined by the relation Ω = m2·kg·s−3·A−2, which follows from the definition of the quantity electrical resistance. The radian and steradian, once given special status, are now considered derived units.
| Quantity | Formula | Symbol (SI Unit) |
|---|---|---|
| Area | A=LxB | m2 |
| Volume | V=LxBXH | m3 |
| Density | D = Mass/Volume | kg m- 3 |
| Velocity | V = Distance/Time | m s-1 |
| Acceleration | a = Change in Velocity/Time | m-2 |
| Momentum | p = mass x velocity | Kg ms-1 |
| Force | F = Mass x Arceleration | N(newton) |
| Work | W = Force x Distance | J(joule) |
| Power | P = Work / Time | W (watt) |
| Potential Energy | P.E. = Force x Displacement = m xg xh | J(joule) |
| Kinetic Energy | KE. = (1/2) x mass x (Velocity)2 | J (joule) |
| Moment of Force | Moment = Force x Perpendicular Distance | Nm |
| Pressure | P = Force / Area | N m-2 or Pa(Pascal) |
It should be noted that while writing the units of a physical quantity
certain guide lines have to be followed:
Use upper case to represent the symbol for a unit named after a scientist.
During its evolution, the metric system has adopted many units of measure. The introduction of SI rationalised both the way in which units of measure were defined and also the list of units in use. These are now catalogued in the official SI Brochure. The table below lists the units of measure in this catalogue and shows the conversion factors connecting them with the equivalent units that were in use on the eve of the adoption of SI.
| Quantity | Dimension | SI unit and symbol | Legacy unit and symbol | Conversion factor |
|---|---|---|---|---|
| Time | T | second (s) | second (s) | 1 |
| Length | L | metre (m) |
centimetre (cm) ångström (Å) |
0.01 10−10 |
| Mass | M | kilogram (kg) | gram (g) | 0.001 |
| Area | L2 | square metre (m2) | are (are) | 100 |
| Acceleration | LT − 2 | (ms−2) | gal (gal) | 10−2 |
| Electric current | I | ampere (A) |
international ampere abampere or biot statampere |
1.000022 10.0 3.335641×10−10 |
| Temperature | Θ | kelvin
(K) degrees Celsius (°C) |
centigrade (°C) |
K = °C + 273.15 1 |
| Luminous intensity | J | candela (cd) | international candle | 0.982 |
| Amount of substance | N | mole (mol) | ||
| Frequency | T − 1 | hertz (Hz) | cycles per second (cps) | 1 |
| Energy | L2MT − 2 | joule (J) | erg (erg) | 10−7 |
| Power | L2MT − 3 | watt (W) | (erg/s) horsepower (HP) Pferdestärke (PS) |
10−7 745.7 735.5 |
| Force | LMT − 2 | newton (N) | dyne (dyn) sthene (sn) kilopond (kp) |
10−5 103 9.80665 |
| Pressure | L − 1MT − 2 | pascal (Pa) | barye (Ba) pieze (pz) atmosphere (at) |
0.1 103 1.0197×10−5 |
| Electric charge | IT | coulomb (C) |
abcoulomb statcoulomb or franklin |
10 3.335641×10−10 |
| Potential difference | L2MT − 3I − 1 | volt (V) | international
volt abvolt statvolt |
1.00034 10−8 2.997925×102 |
| Capacitance | L − 2M − 1T4I2 | farad (F) | abfarad statfarad |
109 1.112650×10−12 |
| Inductance | L2MT − 2I − 2 | henry (H) | abhenry stathenry |
10−9 8.987552×1011 |
| Electric resistance | L2MT − 3I − 2 | ohm (Ω) | international ohm abohm statohm |
1.00049 10−9 8.987552×1011 |
| Electric conductance | L − 2M − 1T3I2 | siemens (S) |
mho (℧) abmho statmho |
0.99951 109 1.112650×10−12 |
| Magnetic flux | L2MT − 2I − 1 | weber (Wb) | maxwell (Mx) | 10−8 |
| Magnetic flux density | MT − 2I − 1 | tesla (T) | gauss (G) | 1×10−4 |
| Magnetic field strength | IL − 2 | (A/m2) | oersted (Oe) | 103/4π = 79.57747 |
| Dynamic viscosity | ML − 1T − 1 | (Pa·s) | poise (P) | 0.1 |
| Kinematic viscosity | L2T − 1 | (m2s−1) | stokes (St) | 10−4 |
| Luminous flux | J | lumen (lm) | stilb (sb) | 104 |
| Illuminance | JL − 2 | lux (lx) | phot (ph) | 104 |
| [Radioactive] activity | T − 1 | bequerel (Bq) | curie (Ci) | 3.70×1010 |
| Absorbed [radiation] dose | L2T − 2 | gray (Gy) |
roentgen (R) rad (rad) |
2.58×10−4 0.01 |
| Radiation dose equivalent | L2T − 2 | sievert | roentgen equivalent man (rem) | 0.01 |
| Catalytic activity | NT − 1 | katal (kat) | No legacy unit | n/a |
The SI brouchure also catalogues certain non-SI units that are widely used with the SI in matters of everyday life or units that are exactly defined values in terms of SI units and are used in particular circumstances to satisfy the needs of commercial, legal, or specialised scientific interests. These units include:
| Quantity | Dimension | Unit and symbol | Equivalence |
|---|---|---|---|
| Mass | M | tonne (t) | 1000 kg |
| Area | L2 | hectare (ha) | 0.01 km2 104 m2 |
| Volume | L3 | litre (L or l) | 0.001 m3 |
| Time | T | minute
(min) hour (h) day (d) |
60 s 3600 s 86400 s |
| Pressure | L − 1MT − 2 | bar | 100 kPa |
| Plane angle | none |
degree (°) minute (ʹ) second (″) |
(π⁄180)
rad (π⁄10800) rad (π⁄648000) rad |
The United States customary system (also called American system or Traditional system of Weights and Measures) is a system of measurement commonly used in the United States. The U.S. is the only industrialized nation that does not mainly use the metric system in its commercial and standards activities, although the International System of Units (SI, often referred to as 'metric') is commonly used in both the US Armed Forces and in fields relating to science, and increasingly in medicine, aviation, government as well as various sectors of industry. The U.S. customary units have roots with the imperial units, which were used in the British Empire.
The system for measuring length is based on the inch, foot, yard, and mile, which are the only four customary length measurements in everyday use. Since July 1, 1959, these have been defined on the basis of 1 yard = 0.9144 meters except for some applications in surveying. This definition was agreed with the UK and other Commonwealth countries, and so is often termed international measure.
| Unit | Divisions | SI Equivalent |
|---|---|---|
|
Exact relationships shown in boldface |
||
| International | ||
| 1 point (p) | 352.8 µm | |
| 1 pica (P) | 12 p | 4.233 mm |
| 1 inch (in) | 6 P | 2.54 cm |
| 1 foot (ft) | 12 in | 0.3048 m |
| 1 yard (yd) | 3 ft | 0.9144 m |
| 1 mile (mi) | 5280 ft | 1.609344 km |
| Survey | ||
| 1 link (li) | 33⁄50 ft or 7.92 in | 2.012 dm |
| 1 (survey) foot (ft) | 1200⁄3937 m | 0.30480061 m |
| 1 rod (rd) | 25 li or 16.5 ft | 5.029210 m |
| 1 chain (ch) | 4 rd | 2.011684 da m |
| 1 furlong (fur) | 10 ch | 2.011 684 hm |
| 1 survey (or statute) mile (mi) | 8 fur | 1.609347 km |
| 1 league (lea) | 3 mi | 4.828042 km |
| Nautical | ||
| 1 fathom (ftm) | 2 yd | 1.8288 m |
| 1 cable (cb) | 120 ftm or 1.091 fur | 2.19456 hm |
| 1 nautical mile (NM or nmi) | 8.439 cb or 1.151 mi | 1.852 km |
The most widely used area unit with a name unrelated to any length unit is the acre. The National Institute of Standards and Technology contends that customary area units are defined in terms of the square survey foot, not the square international foot.
| Unit | Divisions | SI Equivalent |
|---|---|---|
| Exact relationships shown in boldface | ||
| 1 square survey foot (sq ft or ft2) | 144 square inches | 0.09290341 m2 |
| 1 square chain (sq ch) or (ch2) | 4356 feet2 (survey) or 16 sq rods | 404.6873 m2 |
| 1 acre | 43560 sq ft (survey) or 10 sq ch | 4046.873 m2 |
| 1 section | 640 acres or 1 sq mi (survey) | 2.589998 km2 |
| 1 survey township (twp) | 36 sections or 4 sq leagues | 93.23993 km2 |
The cubic inch, cubic foot and cubic yard are commonly used for measuring volume. In addition, there is one group of units for measuring volumes of liquids, and one for measuring volumes of dry material.
Other than the cubic foot, cubic inch and cubic yard, these units are differently sized from the units in the imperial system, although the names of the units are similar. Also, while the U.S. has separate systems for measuring the volumes of liquids and dry material, the imperial system has one set of units for both.
| Volume in general | ||
|---|---|---|
| Unit | Divisions | SI Equivalent |
| 1 cubic inch (cu in) or (in3) | 16.387064 mL | |
| 1 cubic foot (cu ft) or (ft3) | 1728 cu in | 28.31685 L |
| 1 cubic yard (cu yd) or (yd3) | 27 cu ft | 764.559
L 0.7645549 m3 |
| 1 acre-foot (acre ft) | 43560
cu ft 1613.333 cu yd |
1.233482
ML 1233.482 m3 |
One fluid ounce is 1⁄16 of a U.S. pint, 1⁄32 of a U.S. quart, and 1⁄128 of a U.S. gallon. The fluid ounce derives its name originally from being the volume of one ounce avoirdupois of water, but in the U.S. it is defined as 1⁄128 of a U.S. gallon. Consequently, a fluid ounce of water weighs about 1.041 ounces avoirdupois.
There are varying standards for barrel for some specific commodities, including 31 gal for beer, 40 gal for whiskey or kerosene, and 42 gal for petroleum. The general standard for liquids is 31.5 gal or half a hogshead. The common 55 gallon size of drum for storing and transporting various products and wastes is sometimes confused with a barrel, though it is not a standard measure.
In the United States, single servings of beverages are usually measured in fluid ounces. Milk is usually sold in half pints (8 fluid ounces), pints, quarts, half gallons, and gallons. Water volume for sinks, bathtubs, ponds, swimming pools, etc., is usually stated in gallons or cubic feet. Quantities of gases are usually given in cubic feet (at one atmosphere).
Minims, drams and gill are rarely used currently.
| Liquid volume | ||
|---|---|---|
| Most common measures shown in italic font Exact conversions in bold font |
||
| Unit | Divisions | SI Equivalent |
| 1 minim (min) | ~ 1 drop or 0.95 grain of water | 61.61152 μL |
| 1 US fluid dram (fl dr) | 60 min | 3.696691 mL |
| 1 teaspoon (tsp) | 80 min | 4.928921 mL |
| 1 tablespoon (Tbsp) | 3 tsp or 4 fl dr | 14.78676 mL |
| 1 US fluid ounce (fl oz) | 2 Tbsp or 1.041 oz av of water | 29.57353 mL |
| 1 jigger (jig) | 3 Tbsp | 44.36028 mL |
| 1 US gill (gi) | 4 fl oz | 118.2941 mL |
| 1 US cup (cp) | 2 gi or 8 fl oz | 236.5882 mL |
| 1 (liquid) US pint (pt) | 2 cp or 16.65 oz av of water | 473.1765 mL |
| 1 (liquid) US quart (qt) | 2 pt | 0.9463529 L |
| 1 (liquid) US gallon (gal) | 4 qt or 231 cu in | 3.785412 L |
| 1 (liquid) barrel (bbl) | 31.5 gal or 1⁄2 hogshead | 119.2405 L |
| 1 oil barrel (bbl) | 42 gal or 2⁄3 hogshead | 158.9873 L |
| 1 hogshead | 63 gal or 8.421875
cu ft or 524.7 lb of water |
238.4810 L |
Small fruits and vegetables are often sold in dry pints and dry quarts. The U.S. dry gallon is less commonly used, and was not included in the handbook that many states recognize as the authority on measurement law. However pecks, or bushels are sometimes used—particularly for grapes, apples and similar fruits in agricultural regions.
| Dry volume | ||
|---|---|---|
| Unit | Divisions | SI Equivalent |
| 1 (dry) pint (pt) | 33.60 cu in | 0.5506105 L |
| 1 (dry) quart (qt) | 2 pt | 1.101221 L |
| 1 (dry) gallon (gal) | 4 qt or 268.8025 cu in | 4.404884 L |
| 1 peck (pk) | 2 gal | 8.809768 L |
| 1 bushel (bu) | 4 pk or 1.244 cu ft | 35.23907 L |
| 1 (dry) barrel (bbl) | 7056 cu in or 3.281 bu | 115.6271 L |
There have historically been five different English systems of mass: tower, apothecaries', troy, avoirdupois, and metric. Of these, the avoirdupois weight is the most common system used in the U.S., although Troy weight is still used to weigh precious metals. Apothecaries weight—once used by pharmacies—has been largely replaced by metric measurements. Tower weight fell out of use in England (due to legal prohibition in 1527) centuries ago, and was never used in the United States. The imperial system, which is still used for some measures in the U.K. and commonwealth countries, is based on avoirdupois, with variations from U.S. customary units larger than a pound.
The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly 453.59237 grams by agreement between the U.S., the U.K. and other English-speaking countries in 1959. Other units of mass are defined in terms of it.
The avoirdupois pound is legally defined as a measure of mass, but the name pound is also applied to measures of force. For instance, in many contexts, the pound avoirdupois is used as a unit of mass, but in some contexts, the term "pound" is used to refer to "pound-force". The slug is another unit of mass derived from pound-force.
Troy weight, avoirdupois weight, and apothecaries' weight are all built from the same basic unit, the grain, which is the same in all three systems. However, while each system has some overlap in the names of their units of measure (all have ounces and pounds), the relationship between the grain and these other units within each system varies. For example, in apothecary and troy weight, the pound and ounce are the same, but are different from the pound and ounce in avoirdupois in terms of their relationships to grains and to each other. The systems also have different units between the grain and ounce (apothecaries' has scruple and dram, troy has pennyweight, and avoirdupois has just dram, sometimes spelled drachm). The dram in avoirdupois weighs just under half of the dram in apothecaries'. The fluid dram unit of volume is based on the weight of 1 dram of water in the apothecaries' system.
To alleviate confusion, it is typical when publishing non-avoirdupois weights to mention the name of the system along with the unit. Precious metals, for example, are often weighed in "troy ounces", because just "ounce" would be more likely to be assumed to mean an ounce avoirdupois.
For the pound and smaller units, the U.S. customary system and the British imperial system are identical. However, they differ when dealing with units larger than the pound. The definition of the pound avoirdupois in the imperial system is identical to that in the U.S. customary system.
In the United States, only the ounce, pound and short ton—known in the country simply as the ton—are commonly used, though the hundredweight is still used in agriculture and shipping. The grain is used to describe the mass of propellant and projectiles in small arms ammunition. It was also used to measure medicine and other very small masses.
| Unit | Divisions | SI Equivalent |
|---|---|---|
| Most common measures shown in italic font Exact conversions shown in bold font |
||
| Avoirdupois | ||
| 1 grain (gr) | 1⁄7000 lb | 64.79891 mg |
| 1 dram (dr) | 27 11⁄32 gr | 1.7718451953 g |
| 1 ounce (oz) | 16 dr | 28.349523125 g |
| 1 pound (lb) | 16 oz | 453.59237 g |
| 1 US hundredweight (cwt) | 100 lb | 45.359237 kg |
| 1 long hundredweight | 112 lb | 50.80224544 kg |
| 1 short ton | 20 US cwt or 2000 lb | 907.18474 kg |
| 1 long ton | 20 long cwt or 2240 lb | 1016.0469088 kg |
| Troy | ||
| 1 grain (gr) | 1⁄7000 lb av or 1⁄5760 lb t | 64.79891 mg |
| 1 pennyweight (dwt) | 24 gr or 7.776 carats | 1.55517384 g |
| 1 troy ounce (oz t) | 20 dwt | 31.1034768 g |
| 1 troy pound (lb t) | 12 oz t or 13.17 oz av | 373.2417216 g |
Degrees Fahrenheit are used in the United States to measure temperatures in most non-scientific contexts. The Rankine scale of absolute temperature also saw some use in thermodynamics. Scientists worldwide use the kelvin and degree Celsius. Several technical standards are expressed in Fahrenheit temperatures and U.S. medical practitioners often use degrees Fahrenheit for body temperature.
The relationship between the different temperature scales is linear, but the scales have different zero points so that conversion is not simply multiplication by a factor: pure water is defined to freeze at 32 °F = 0 °C and boil at 212 °F = 100 °C at 1 atm; the conversion formula is easily shown to be: F = 32 + 9C/5 or inversely as C = 5 (F-32)/9
British law now defines each imperial unit in terms of the metric equivalent. The metric system is in official use within the United Kingdom for some applications; however, use of Imperial unit is widespread in many cases. The Imperial units refer to the post-1824 measures used in the British Empire and countries in the British sphere of influence. The system of units used in England before 1824 are know as the English units. By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement.
Since 1959, the US and the British yard have been defined identically to be 0.9144 metres, to match the international yard. Metric equivalents in this article usually assume this latest official definition. Before this date, the most precise measurement of the Imperial Standard Yard was 0.914398416 metres.
| Unit | Relative to previous | Feet | Millimetres | Metres | Notes |
|---|---|---|---|---|---|
| thou (th) | 1⁄12000 | 0.0254 | 0.000 025 4 | 25.4 μm | |
| inch (in) | 1000 thou | 1⁄12 | 25.4 | 0.025 4 | |
| foot (ft) | 12 inches | 1 | 304.8 | 0.3048 | |
| yard (yd) | 3 feet | 3 | 914.4 | 0.9144 | Defined as exactly 0.9144 metres since 1959 |
| chain (ch) | 22 yards | 66 | 20116.8 | 20.1168 | |
| furlong (fur) | 10 chains | 660 | 201.168 | ||
| mile (mi) | 8 furlongs | 5,280 | 1,609.344 | ||
| league (lea) | 3 miles | 15,840 | 4,828.032 | No longer an official unit in any nation. | |
| Maritime units | |||||
| fathom (ftm) | ~2 yards | 6.08 or 6 | 1,853.184 | 1.853184 | The British Admiralty in practice used a fathom as 6 feet. This was despite its being 1⁄1000 of a nautical mile (i.e. 6.08 feet) until the adoption of the international nautical mile. The commonly accepted definition of a fathom was always 6 feet. The conflict was inconsequential as Admiralty nautical charts designated depths shallower than 5 fathoms in feet on older imperial charts. Today all charts worldwide are metric, except for USA Hydrographic Office charts, which use feet for all depth ranges. |
| cable | 100 fathoms | 608 | 185.3184 | One tenth of a nautical mile. When in use it was approximated colloquially as 100 fathoms. | |
| nautical mile | 10 cables | 6,080 | 1,853.184 | Used to measure distances at sea. Until the adoption of the international definition of 1852 metres in 1970, the British nautical (Admiralty) mile was defined as 6,080 feet. It was not readily expressible in terms of any of the intermediate units, because it was derived from the circumference of the Earth (like the original metre). | |
| Gunter's survey units (17th century onwards) | |||||
| link | 7.92 inches | 66⁄100 | 201.168 | 0.201168 | 1⁄100 of a chain |
| rod | 25 links | 66⁄4 | 5,029.2 | 5.0292 | The rod is also called pole or perch. |
| chain | 4 rods | 66 | 20.1168 | 1⁄10 of a furlong | |
| Unit | Relation to units of length | Square feet | Square rods | Square miles | Square metres | Hectares | Notes |
|---|---|---|---|---|---|---|---|
| perch | 1 rod × 1 rod | 272.25 | 1 | 1⁄102400 | 25.29285264 | 0.002529 | Although the proper term is square rod, for centuries this unit has been called a pole or perch or, more properly square pole or square perch. |
| rood | 1 furlong × 1 rod | 10,890 | 40 | 1⁄2560 | 1,011.7141056 | 0.1012 | The rood is also called a rod. It is 1,210 square yards. |
| acre | 1 furlong × 1 chain | 43,560 | 160 | 1⁄640 | 4,046.8564224 | 0.4047 | One acre is 4,840 square yards |
| Note: All equivalences are exact except the hectares, which are accurate to four significant figures. | |||||||
In 1824, the United Kingdom adopted a close approximation to the ale gallon known as the imperial gallon. The imperial gallon was based on the volume of 10 lb of distilled water weighed in air with brass weights with the barometer standing at 30 in Hg at a temperature of 62 °F. In 1963 this definition was refined as the space occupied by 10 lb of distilled water of density 0.998859 g/mL weighed in air of density 0.001217 g/mL against weights of density 8.136 g/mL. This works out to 4.546096 L, or 277.4198 cu in. The Weights and Measures Act of 1985 switched to a gallon of exactly 4.54609 L (approximately 277.4194 cu in).
| Unit | Imperial ounce | Imperial pint | Millilitres | Cubic inches | US ounces | US pints |
|---|---|---|---|---|---|---|
| fluid ounce (fl oz) | 1 | 1⁄20 | 28.4130625 | 1.7339 | 0.96076 | 0.060047 |
| gill (gi) | 5 | 1⁄4 | 142.0653125 | 8.6694 | 4.8038 | 0.30024 |
| pint (pt) | 20 | 1 | 568.26125 | 34.677 | 19.215 | 1.2009 |
| quart (qt) | 40 | 2 | 1,136.5225 | 69.355 | 38.430 | 2.4019 |
| gallon (gal) | 160 | 8 | 4,546.09 | 277.42 | 153.72 | 9.6076 |
| Note: The millilitre equivalences are exact whereas the conversions to cubic-inch and US measures are correct to five significant figures. | ||||||
In the 19th and 20th centuries the UK used three different systems for mass and weight:
The troy pound (373.2417216 g) was made the primary unit of mass by the 1824 Act; however, its use was abolished in the UK on 6 January 1879, making the Avoirdupois pound the primary unit of mass with only the troy ounce (31.1034768 g) and its decimal subdivisions retained. In all the systems, the fundamental unit is the pound, and all other units are defined as fractions or multiples of it.
| Unit | Pounds | Grams | Kilograms | Notes |
|---|---|---|---|---|
| grain (gr) | 1⁄7000 | 0.06479891 | Exactly 64.79891 milligrams. | |
| drachm (drc) | 1⁄256 | 1.7718451953125 | ||
| ounce (oz) | 1⁄16 | 28.349523125 | ||
| pound (lb) | 1 | 453.59237 | 0.45359237 | Exactly 453.59237 grams by definition. |
| stone (st) | 14 | 6,350.29318 | 6.35029318 | A person's weight is often quoted in stone and pounds in English-speaking countries using the avoirdupois system, with the exception of the United States and Canada, where it is usually quoted in pounds. |
| quarter (qtr) | 28 | 12.70058636 | One quarter is equal to two stone or a quarter of a hundredweight. The term quarter was also commonly used to refer to a quarter of a pound in a retail context. | |
| hundredweight (cwt) | 112 | 50.80234544 | One imperial hundredweight is equal to eight stone. This is the long hundredweight as opposed to the short hundredweight of 100 pounds as used in the United States. | |
| ton (t) | 2240 | 1,016.0469088 | As with the US system twenty hundredweights equal a ton. However, since the imperial hundredweight is 12% greater than the US equivalent, the imperial ton (or long ton) is 2,240 pounds, which is very close to a tonne, compared to the short ton of 2,000 pounds (907.185 kg). |
For each physical quantity, a number of different units (some only of historical interest) are shown and expressed in terms of the corresponding SI unit.
| Symbol | Definition |
|---|---|
| ≡ | exactly equal to |
| ≈ | approximately equal to |
| digits | indicates that digits repeat infinitely (e.g. 8.294369 corresponds to 8.294369369369369…) |
| (H) | of chiefly historical interest |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| angstrom | Å | ≡ 1×10−10 m | ≡ 0.1 nm |
| astronomical unit | AU | ≈ Distance from Earth to Sun | ≈ 149597871464 m |
| barleycorn (H) | = ⅓ in (see note above about rounding) | ≈ 8.46×10−3 m | |
| bohr, atomic unit of length | a0 | ≡ Bohr radius of hydrogen | ≈ 5.2917720859×10−11 ± 3.6×10−20 m |
| cable length (imperial) | ≡ 608 ft | ≈ 185.3184 m | |
| cable length (International) | ≡ 1/10 nmi | ≡ 185.2 m | |
| cable length (US) | ≡ 720 ft | = 219.456 m | |
| chain (Gunter's; Surveyor's) | ch | ≡ 66 ft(US) ≡ 4 rods | ≈ 20.11684 m |
| cubit (H) | ≡ Distance from fingers to elbow ≈ 18 in | ≈ 0.5 m | |
| ell (H) | ell | ≡ 45 in (In England usually) | = 1.143 m |
| fathom | fm | ≡ 6 ft | = 1.8288 m |
| fermi | fm | ≡ 1×10−15 m | ≡ 1×10−15 m |
| finger | ≡ 7/8 in | = 0.022225 m | |
| finger (cloth) | ≡ 4½ in | = 0.1143 m | |
| foot (Benoît) (H) | ft (Ben) | ≈ 0.304799735 m | |
| foot (Clarke's; Cape) (H) | ft (Cla) | ≈ 0.3047972654 m | |
| foot (Indian) (H) | ft Ind | ≈ 0.304799514 m | |
| foot (International) | ft | ≡ 1/3 yd ≡ 0.3048 m ≡ 12 inches | ≡ 0.3048 m |
| foot (Sear's) (H) | ft (Sear) | ≈ 0.30479947 m | |
| foot (US Survey) | ft (US) | ≡ 1200⁄3937 m | ≈ 0.304800610 m |
| french; charriere | F | ≡ 1⁄3 mm | = 0.3 ×10−3 m |
| furlong | fur | ≡ 10 chains = 660 ft = 220 yd | = 201.168 m |
| hand | ≡ 4 in | ≡ 0.1016 m | |
| inch (International) | in | ≡ 1/36 yd ≡ 1/12 ft | ≡ 0.0254 m |
| league (land) | lea | ≡ 3 US Statute miles | = 4828.032 m |
| light-day | ≡ 24 light-hours | ≡ 2.59020683712×1013 m | |
| light-hour | ≡ 60 light-minutes | ≡ 1.0792528488×1012 m | |
| light-minute | ≡ 60 light-seconds | ≡ 1.798754748×1010 m | |
| light-second | ≡ Distance light travels in one second in vacuum | ≡ 299792458 m | |
| light-year | ly | ≡ Distance light travels in vacuum in 365.25 days | = 9.4607304725808×1015 m |
| line | ln | ≡ 1/12 in | = 0.002116 m |
| link (Gunter's; Surveyor's) | lnk | ≡ 1/100 ch ≡ 0.66 ft ≡ 7.92in | = 0.201168 m |
| link (Ramsden's; Engineer's) | lnk | ≡ 1 ft | = 0.3048 m |
| metre (SI base unit) | m | ≡ Distance light travels in 1⁄299792458
of a second in vacuum. ≈ 1⁄10000000 of the distance from equator to pole. |
≡ 1 m |
| mickey | ≡ 1⁄200 in | = 1.27×10−4 m | |
| micron | µ | ≡ 1×10−6 m | |
| mil; thou | mil | ≡ 1×10−3 in | ≡ 2.54×10−5 m |
| mil (Sweden and Norway) | mil | ≡ 10 km | = 10000 m |
| mile (geographical) (H) | ≡ 6082 ft | = 1853.7936 m | |
| mile (international) | mi | ≡ 80 chains ≡ 5280 ft ≡ 1760 yd | ≡ 1609.344 m |
| mile (tactical or data) | ≡ 6000 ft | ≡ 1828.8 m | |
| mile (telegraph) (H) | mi | ≡ 6087 ft | = 1855.3176 m |
| mile (US Survey) | mi | ≡ 5280 US Survey feet ≡ (5280 × 1200⁄3937) m | ≈ 1609.347219 m |
| nail (cloth) | ≡ 2¼ in | = 0.057 15 m | |
| nanometer | nm | ≡ 1×10−9 m | ≡ 1×10−9 m |
| nautical league | NL; nl | ≡ 3 nmi | = 5556 m |
| nautical mile (Admiralty) | NM (Adm); nmi (Adm) | = 6080 ft | = 1853.184 m |
| nautical mile (international) | NM; nmi | ≡ 1852 m | ≡ 1852 m |
| nautical mile (US pre 1954) | ≡ 1853.248 m | ≡ 1853.248 m | |
| pace | ≡ 2.5 ft | = 0.762 m | |
| palm | ≡ 3 in | = 0.0762 m | |
| parsec | pc | Distance of star with parallax shift of one arc second from a base of one astronomical unit | ≈ 3.085 677 82×1016 ± 6×106 m |
| pica | ≡ 12 points | Dependent on point measures. | |
| point (American, English) | pt | ≡ 1/72.272 in | ≈ 0.000 351 450 m |
| point (Didot; European) | pt | ≡ 1/12 × 1/72 of
pied du roi; After 1878: ≡ 5/133 cm |
≈ 0.000 375 97 m; After 1878: ≈ 0.000 375 939 85 m |
| point (PostScript) | pt | ≡ 1/72 in | = 0.000 352 7 m |
| point (TeX) | pt | ≡ 1/72.27 in | = 0.000 351 4598 m |
| quarter | ≡ ¼ yd | = 0.2286 m | |
| rod; pole; perch (H) | rd | ≡ 16½ ft | = 5.0292 m |
| rope (H) | rope | ≡ 20 ft | = 6.096 m |
| span (H) | ≡ 9 in | = 0.2286 m | |
| spat | ≡ 1×1012 m | ||
| stick (H) | ≡ 2 in | = 0.0508 m | |
| stigma; bicron (picometre) | pm | ≡ 1×10−12 m | |
| twip | twp | ≡ 1/1440 in | = 1.7638×10−5 m |
| x unit; siegbahn | xu | ≈ 1.0021×10−13 m | |
| yard (International) | yd | ≡ 0.9144 m ≡ 3 ft ≡ 36 in | ≡ 0.9144 m |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| acre (international) | ac | ≡ 1 ch × 10 ch = 4840 sq yd | ≡ 4 046.856 4224 m2 |
| acre (U. S. survey) | ac | ≡ 10 sq ch = 4840 sq yd, also 43560 sq ft. | ≈ 4 046.873 m2 |
| are | a | ≡ 100 m2 | = 100 m2 |
| barn | b | ≡ 10−28 m2 | = 10−28 m2 |
| barony | ≡ 4000 ac | ≈ 1.618 742×107 m2 | |
| board | bd | ≡ 1 in × 1 ft | = 7.741 92×10−3 m2 |
| boiler horsepower equivalent direct radiation | bhp EDR | ≡ (1 ft2) (1 bhp) / (240 BTUIT/h) | ≈ 12.958 174 m2 |
| circular inch | circ in | ≡ π/4 sq in | ≈ 5.067 075×10−4 m2 |
| circular mil; circular thou | circ mil | ≡ π/4 mil2 | ≈ 5.067 075×10−10 m2 |
| cord | ≡ 192 bd | = 1.486 448 64 m2 | |
| dunam | ≡ 1 000 m2 | = 1 000 m2 | |
| guntha | ≡ 121 sq yd | ≈ 101.17 m2 | |
| hectare | ha | ≡ 10 000 m2 | ≡ 10 000 m2 |
| hide | ≈ 120 ac (variable) | ≈ 5×105 m2 | |
| rood | ro | ≡ ¼ ac | = 1 011.714 1056 m2 |
| section | ≡ 1 mi × 1 mi | = 2.589 988 110 336×106 m2 | |
| shed | ≡ 10−52 m2 | = 10−52 m2 | |
| square (roofing) | ≡ 10 ft × 10 ft | = 9.290 304 m2 | |
| square chain (international) | sq ch | ≡ 66 ft × 66 ft = 1/10 ac | ≡ 404.685 642 24 m2 |
| square chain (US Survey) | sq ch | ≡ 66 ft(US) × 66 ft(US) = 1/10 ac | ≈ 404.687 3 m2 |
| square foot | sq ft | ≡ 1 ft × 1 ft | ≡ 9.290 304×10−2 m2 |
| square foot (US Survey) | sq ft | ≡ 1 ft (US) × 1 ft (US) | ≈ 9.290 341 161 327 49×10−2 m2 |
| square inch | sq in | ≡ 1 in × 1 in | ≡ 6.4516×10−4 m2 |
| square kilometre | km2 | ≡ 1 km × 1 km | = 106 m2 |
| square link (Gunter's)(International) | sq lnk | ≡ 1 lnk × 1 lnk ≡ 0.66 ft × 0.66 ft | = 4.046 856 4224×10−2 m2 |
| square link (Gunter's)(US Survey) | sq lnk | ≡ 1 lnk × 1 lnk ≡ 0.66 ft(US) × 0.66 ft(US) | ≈ 4.046 872×10−2 m2 |
| square link (Ramsden's) | sq lnk | ≡ 1 lnk × 1 lnk ≡ 1 ft × 1 ft | = 0.09290304 m2 |
| square metre (SI unit) | m2 | ≡ 1 m × 1 m | = 1 m2 |
| square mil; square thou | sq mil | ≡ 1 mil × 1 mil | = 6.4516×10−10 m2 |
| square mile | sq mi | ≡ 1 mi × 1 mi | = 2.589 988 110 336×106 m2 |
| square mile (US Survey) | sq mi | ≡ 1 mi (US) × 1 mi (US) | ≈ 2.589 998 47×106 m2 |
| square rod/pole/perch | sq rd | ≡ 1 rd × 1 rd | = 25.292 852 64 m2 |
| square yard (International) | sq yd | ≡ 1 yd × 1 yd | ≡ 0.836 127 36 m2 |
| stremma | ≡ 1 000 m2 | = 1 000 m2 | |
| township | ≡ 36 sq mi (US) | ≈ 9.323 994×107 m2 | |
| yardland | ≈ 30 ac | ≈ 1.2×105 m2 |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| acre-foot | ac ft | ≡ 1 ac x 1 ft = 43 560 ft3 | = 1 233.481 837 547 52 m3 |
| acre-inch | ≡ 1 ac × 1 in | = 102.790 153 128 96 m3 | |
| barrel (imperial) | bl (imp) | ≡ 36 gal (imp) | = 0.163 659 24 m3 |
| barrel (petroleum) | bl; bbl | ≡ 42 gal (US) | = 0.158 987 294 928 m3 |
| barrel (US dry) | bl (US) | ≡ 105 qt (US) = 105/32 bu (US lvl) | = 0.115 628 198 985 075 m3 |
| barrel (US fluid) | fl bl (US) | ≡ 31½ gal (US) | = 0.119 240 471 196 m3 |
| board-foot | fbm | ≡ 144 cu in | ≡ 2.359 737 216×10−3 m3 |
| bucket (imperial) | bkt | ≡ 4 gal (imp) | = 0.018 184 36 m3 |
| bushel (imperial) | bu (imp) | ≡ 8 gal (imp) | = 0.036 368 72 m3 |
| bushel (US dry heaped) | bu (US) | ≡ 1 ¼ bu (US lvl) | = 0.044 048 837 7086 m3 |
| bushel (US dry level) | bu (US lvl) | ≡ 2 150.42 cu in | = 0.035 239 070 166 88 m3 |
| butt, pipe | ≡ 126 gal (wine) | = 0.476 961 884 784 m3 | |
| coomb | ≡ 4 bu (imp) | = 0.145 474 88 m3 | |
| cord (firewood) | ≡ 8 ft × 4 ft × 4 ft | = 3.624 556 363 776 m3 | |
| cord-foot | ≡ 16 cu ft | = 0.453 069 545 472 m3 | |
| cubic fathom | cu fm | ≡ 1 fm × 1 fm × 1 fm | = 6.116 438 863 872 m3 |
| cubic foot | cu ft | ≡ 1 ft × 1 ft × 1 ft | ≡ 0.028 316 846 592 m3 |
| cubic inch | cu in | ≡ 1 in × 1 in × 1 in | ≡ 16.387 064×10−6 m3 |
| cubic metre (SI unit) | m3 | ≡ 1 m × 1 m × 1 m | ≡ 1 m3 |
| cubic mile | cu mi | ≡ 1 mi × 1 mi × 1 mi | ≡ 4 168 181 825.440 579 584 m3 |
| cubic yard | cu yd | ≡ 27 cu ft | ≡ 0.764 554 857 984 m3 |
| cup (breakfast) | ≡ 10 fl oz (imp) | = 284.130 625×10−6 m3 | |
| cup (Canadian) | c (CA) | ≡ 8 fl oz (imp) | = 227.3045×10−6 m3 |
| cup (metric) | c | ≡ 250.0×10−6 m3 | = 250.0×10−6 m3 |
| cup (US customary) | c (US) | ≡ 8 US fl oz ≡ 1/16 gal (US) | = 236.588 2365×10−6 m3 |
| cup (US food nutrition labeling) | c (US) | ≡ 240 mL | = 2.4×10−4 m3 |
| dash (imperial) | ≡ 1/384 gi (imp) = ½ pinch (imp) | = 369.961 751 302 08 3×10−9 m3 | |
| dash (US) | ≡ 1/96 US fl oz = ½ US pinch | = 308.057 599 609 375×10−9 m3 | |
| dessertspoon (imperial) | ≡ 1/12 gi (imp) | = 11.838 776 0416×10−6 m3 | |
| drop (imperial) | gtt | ≡ 1/288 fl oz (imp) | = 98.656 467 013 8×10−9 m3 |
| drop (imperial) (alt) | gtt | ≡ 1/1 824 gi (imp) | ≈ 77.886 684×10−9 m3 |
| drop (medical) | ≡ 1/12 ml | = 83.03×10−9 m3 | |
| drop (metric) | ≡ 1/20 mL | = 50.0×10−9 m3 | |
| drop (US) | gtt | ≡ 1/360 US fl oz | = 82.148 693 22916×10−9 m3 |
| drop (US) (alt) | gtt | ≡ 1/456 US fl oz | ≈ 64.854 231×10−9 m3 |
| fifth | ≡ 1/5 US gal | = 757.082 3568×10−6 m3 | |
| firkin | ≡ 9 gal (US) | = 0.034 068 706 056 m3 | |
| fluid drachm (imperial) | fl dr | ≡ ⅛ fl oz (imp) | = 3.551 632 8125×10−6 m3 |
| fluid dram (US); US fluidram | fl dr | ≡ ⅛ US fl oz | = 3.696 691 195 3125×10−6 m3 |
| fluid scruple (imperial) | fl s | ≡ 1/24 fl oz (imp) | = 1.183 877 60416×10−6 m3 |
| gallon (beer) | beer gal | ≡ 282 cu in | = 4.621 152 048×10−3 m3 |
| gallon (imperial) | gal (imp) | ≡ 4.546 09 L | ≡ 4.546 09×10−3 m3 |
| gallon (US dry) | gal (US) | ≡ ⅛ bu (US lvl) | = 4.404 883 770 86×10−3 m3 |
| gallon (US fluid; Wine) | gal (US) | ≡ 231 cu in | ≡ 3.785 411 784×10−3 m3 |
| gill (imperial); Noggin | gi (imp); nog | ≡ 5 fl oz (imp) | = 142.065 3125×10−6 m3 |
| gill (US) | gi (US) | ≡ 4 US fl oz | = 118.294 118 25×10−6 m3 |
| hogshead (imperial) | hhd (imp) | ≡ 2 bl (imp) | = 0.327 318 48 m3 |
| hogshead (US) | hhd (US) | ≡ 2 fl bl (US) | = 0.238 480 942 392 m3 |
| jigger (bartending) | ≡ 1½ US fl oz | ≈ 44.36×10−6 m3 | |
| kilderkin | ≡ 18 gal (imp) | = 0.081 829 62 m3 | |
| lambda | λ | ≡ 1 mm3 | = 1×10−9 m3 |
| last | ≡ 80 bu (imp) | = 2.909 4976 m3 | |
| litre | L | ≡ 1 dm3 | ≡ 0.001 m3 |
| load | ≡ 50 cu ft | = 1.415 842 3296 m3 | |
| minim (imperial) | min | ≡ 1/480 fl oz (imp) = 1/60 fl dr (imp) | = 59.193 880 208 3×10−9 m3 |
| minim (US) | min | ≡ 1/480 US fl oz = 1/60 US fl dr | = 61.611 519 921 875×10−9 m3 |
| ounce (fluid imperial) | fl oz (imp) | ≡ 1/160 gal (imp) | ≡ 28.413 0625×10−6 m3 |
| ounce (fluid US customary) | US fl oz | ≡ 1/128 gal (US) | ≡ 29.573 529 5625×10−6 m3 |
| ounce (fluid US food nutrition labeling) | US fl oz | ≡ 30 mL | ≡ 3×10−5 m3 |
| peck (imperial) | pk | ≡ 2 gal (imp) | = 9.092 18×10−3 m3 |
| peck (US dry) | pk | ≡ ¼ US lvl bu | = 8.809 767 541 72×10−3 m3 |
| perch | per | ≡ 16½ ft × 1½ ft × 1 ft | = 0.700 841 953 152 m3 |
| pinch (imperial) | ≡ 1/192 gi (imp) = ⅛ tsp (imp) | = 739.923 502 60416×10−9 m3 | |
| pinch (US) | ≡ 1/48 US fl oz = ⅛ US tsp | = 616.115 199 218 75×10−9 m3 | |
| pint (imperial) | pt (imp) | ≡ ⅛ gal (imp) | = 568.261 25×10−6 m3 |
| pint (US dry) | pt (US dry) | ≡ 1/64 bu (US lvl) ≡ ⅛ gal (US dry) | = 550.610 471 3575×10−6 m3 |
| pint (US fluid) | pt (US fl) | ≡ ⅛ gal (US) | = 473.176 473×10−6 m3 |
| pony | ≡ 3/4 US fl oz | = 22.180 147 171 875×10−6 m3 | |
| pottle; quartern | ≡ ½ gal (imp) = 80 fl oz (imp) | = 2.273 045×10−3 m3 | |
| quart (imperial) | qt (imp) | ≡ ¼ gal (imp) | = 1.136 5225×10−3 m3 |
| quart (US dry) | qt (US) | ≡ 1/32 bu (US lvl) = ¼ gal (US dry) | = 1.101 220 942 715×10−3 m3 |
| quart (US fluid) | qt (US) | ≡ ¼ gal (US fl) | = 946.352 946×10−6 m3 |
| quarter; pail | ≡ 8 bu (imp) | = 0.290 949 76 m3 | |
| register ton | ≡ 100 cu ft | = 2.831 684 6592 m3 | |
| sack (imperial); bag | ≡ 3 bu (imp) | = 0.109 106 16 m3 | |
| sack (US) | ≡ 3 bu (US lvl) | = 0.105 717 210 500 64 m3 | |
| seam | ≡ 8 bu (US lvl) | = 0.281 912 561 335 04 m3 | |
| shot | ≡ 1 US fl oz | ≈ 29.57×10−6 m3 | |
| strike (imperial) | ≡ 2 bu (imp) | = 0.072 737 44 m3 | |
| strike (US) | ≡ 2 bu (US lvl) | = 0.070 478 140 333 76 m3 | |
| tablespoon (Australian metric) | ≡ 20.0×10−6 m3 | ||
| tablespoon (Canadian) | tbsp | ≡ ½ fl oz (imp) | = 14.206 531 25×10−6 m3 |
| tablespoon (imperial) | tbsp | ≡ 5/8 fl oz (imp) | = 17.758 164 0625×10−6 m3 |
| tablespoon (metric) | ≡ 15.0×10−6 m3 | ||
| tablespoon (US customary) | tbsp | ≡ ½ US fl oz | = 14.786 764 7825×10−6 m3 |
| tablespoon (US food nutrition labeling) | tbsp | ≡ 15 mL | = 1.5×10−5 m3 |
| teaspoon (Canadian) | tsp | ≡ 1/6 fl oz (imp) | = 4.735 510 416×10−6 m3 |
| teaspoon (imperial) | tsp | ≡ 1/24 gi (imp) | = 5.919 388 02083×10−6 m3 |
| teaspoon (metric) | ≡ 5.0×10−6 m3 | = 5.0×10−6 m3 | |
| teaspoon (US customary) | tsp | ≡ 1/6 US fl oz | = 4.928 921 595×10−6 m3 |
| teaspoon (US food nutrition labeling) | tsp | ≡ 5 mL | = 5×10−6 m3 |
| timber foot | ≡ 1 cu ft | = 0.028 316 846 592 m3 | |
| ton (displacement) | ≡ 35 cu ft | = 0.991 089 630 72 m3 | |
| ton (freight) | ≡ 40 cu ft | = 1.132 673 863 68 m3 | |
| ton (water) | ≡ 28 bu (imp) | = 1.018 324 16 m3 | |
| tun | ≡ 252 gal (wine) | = 0.953 923 769 568 m3 | |
| wey (US) | ≡ 40 bu (US lvl) | = 1.409 562 806 6752 m3 |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| angular mil | µ | ≡ 2π/6400 rad | ≈ 0.981 748×10−3 rad |
| arcminute; MOA | ' | ≡ 1°/60 | ≈ 0.290 888×10−3 rad |
| arcsecond | " | ≡ 1°/3600 | ≈ 4.848 137×10−6 rad |
| centesimal minute of arc | ' | ≡ 1 grad/100 | ≈ 0.157 080×10−3 rad |
| centesimal second of arc | " | ≡ 1 grad/(10 000) | ≈ 1.570 796×10−6 rad |
| degree (of arc) | ° | ≡ 1/360 of a revolution ≡ π/180 rad | ≈ 17.453 293×10−3 rad |
| grad; gradian; gon | grad | ≡ 1/400 of a revolution ≡ 2π/400 rad ≡ 0.9° | ≈ 15.707 963×10−3 rad |
| octant | ≡ 45° | ≈ 0.785 398 rad | |
| quadrant | ≡ 90° | ≈ 1.570 796 rad | |
| radian (SI unit) | rad | The angle subtended at the center of a circle by an arc whose length is equal to the circle's radius. One full revolution encompasses 2π radians. | = 1 rad |
| sextant | ≡ 60° | ≈ 1.047 198 rad | |
| sign | ≡ 30° | ≈ 0.523 599 rad |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| steradian (SI unit) | sr | The solid angle subtended at the center of a sphere of radius r by a portion of the surface of the sphere having an area r2. A sphere encompasses 4π sr. | = 1 sr |
Notes:
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| atomic mass unit, unified | u; AMU | ≈ 1.660 538 73×10−27 ± 1.3×10−36 kg | |
| atomic unit of mass, electron rest mass | me | ≈ 9.109 382 15×10−31 ± 45×10−39 kg | |
| bag (coffee) | ≡ 60 kg | = 60 kg | |
| bag (Portland cement) | ≡ 94 lb av | = 42.637 682 78 kg | |
| barge | ≡ 22½ sh tn | = 20 411.656 65 kg | |
| carat | kt | ≡ 3 1/6 gr | ≈ 205.196 548 333 mg |
| carat (metric) | ct | ≡ 200 mg | = 200 mg |
| clove | ≡ 8 lb av | = 3.628 738 96 kg | |
| crith | ≈ 89.9349 mg | ||
| dalton | Da | ≈ 1.660 902 10×10−27 ± 1.3×10−36 kg | |
| dram (apothecary; troy) | dr t | ≡ 60 gr | = 3.887 9346 g |
| dram (avoirdupois) | dr av | ≡ 27 11/32 gr | = 1.771 845 195 3125 g |
| electronvolt | eV | ≡ 1 eV (energy unit) / c2 | = 1.7826×10−36 kg |
| gamma | γ | ≡ 1 μg | = 1 μg |
| grain | gr | ≡ 1/7000 lb av | ≡ 64.798 91 mg |
| grave | G | grave was the original name of the kilogram | ≡ 1 kg |
| hundredweight (long) | long cwt or cwt | ≡ 112 lb av | = 50.802 345 44 kg |
| hundredweight (short); cental | sh cwt | ≡ 100 lb av | = 45.359 237 kg |
| kilogram | kg | ≡ mass of the prototype near Paris (≈ mass of 1L of water) | ≡ 1 kg (SI base unit) |
| kip | kip | ≡ 1000 lb av | = 453.592 37 kg |
| mark | ≡ 8 oz t | = 248.827 8144 g | |
| mite | ≡ 1/20 gr | = 3.239 9455 mg | |
| mite (metric) | ≡ 1/20 g | = 50 mg | |
| ounce (apothecary; troy) | oz t | ≡ 1/12 lb t | = 31.103 4768 g |
| ounce (avoirdupois) | oz av | ≡ 1/16 lb | = 28.349 523 125 g |
| ounce (US food nutrition labeling) | oz | ≡ 28 g | = 28 g |
| pennyweight | dwt; pwt | ≡ 1/20 oz t | = 1.555 173 84 g |
| point | ≡ 1/100 ct | = 2 mg | |
| pound | lb | ≡ slug·ft/s2 | = 0.45359237 kg |
| pound (avoirdupois) | lb av | ≡ 0.453 592 37 kg = 7000 grains | ≡ 0.453 592 37 kg |
| pound (metric) | ≡ 500 g | = 500 g | |
| pound (troy) | lb t | ≡ 5 760 grains | = 0.373 241 7216 kg |
| quarter (imperial) | ≡ 1/4 long cwt = 2 st = 28 lb av | = 12.700 586 36 kg | |
| quarter (informal) | ≡ ¼ short tn | = 226.796 185 kg | |
| quarter, long (informal) | ≡ ¼ long tn | = 254.011 7272 kg | |
| quintal (metric) | q | ≡ 100 kg | = 100 kg |
| scruple (apothecary) | s ap | ≡ 20 gr | = 1.295 9782 g |
| sheet | ≡ 1/700 lb av | = 647.9891 mg | |
| slug; geepound; hyl | slug | ≡ 1 gee × 1 lb av × 1 s2/ft | ≈ 14.593 903 kg |
| stone | st | ≡ 14 lb av | = 6.350 293 18 kg |
| ton, assay (long) | AT | ≡ 1 mg × 1 long tn ÷ 1 oz t | ≈ 32.666 667 g |
| ton, assay (short) | AT | ≡ 1 mg × 1 sh tn ÷ 1 oz t | ≈ 29.166 667 g |
| ton, long | long tn or ton | ≡ 2 240 lb | = 1 016.046 9088 kg |
| ton, short | sh tn | ≡ 2 000 lb | = 907.184 74 kg |
| tonne (mts unit) | t | ≡ 1 000 kg | = 1 000 kg |
| wey | ≡ 252 lb = 18 st | = 114.305 277 24 kg (variants exist) | |
| Zentner | Ztr. | Definitions vary; see and. |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| gram per millilitre | g/mL | ≡ g/mL | = 1,000 kg/m3 |
| kilogram per cubic metre (SI unit) | kg/m3 | ≡ kg/m3 | = 1 kg/m3 |
| kilogram per litre | kg/L | ≡ kg/L | = 1,000 kg/m3 |
| ounce (avoirdupois) per cubic foot | oz/ft3 | ≡ oz/ft3 | ≈ 1.001153961 kg/m3 |
| ounce (avoirdupois) per cubic inch | oz/in3 | ≡ oz/in3 | ≈ 1.729994044×103 kg/m3 |
| ounce (avoirdupois) per gallon (imperial) | oz/gal | ≡ oz/gal | ≈ 6.236023291 kg/m3 |
| ounce (avoirdupois) per gallon (US fluid) | oz/gal | ≡ oz/gal | ≈ 7.489151707 kg/m3 |
| pound (avoirdupois) per cubic foot | lb/ft3 | ≡ lb/ft3 | ≈ 16.01846337 kg/m3 |
| pound (avoirdupois) per cubic inch | lb/in3 | ≡ lb/in3 | ≈ 2.767990471×104 kg/m3 |
| pound (avoirdupois) per gallon (imperial) | lb/gal | ≡ lb/gal | ≈ 99.77637266 kg/m3 |
| pound (avoirdupois) per gallon (US fluid) | lb/gal | ≡ lb/gal | ≈ 119.8264273 kg/m3 |
| slug per cubic foot | slug/ft3 | ≡ slug/ft3 | ≈ 515.3788184 kg/m3 |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| atomic unit of time | au | ≡ a0/(α·c) | ≈ 2.418 884 254×10−17 s |
| Callippic cycle | ≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d | = 2.398 3776×109 s | |
| century | c | ≡ 100 a (see below for definition of year length) | = 100 years |
| day | d | = 24 h | = 1440 min = 86400 s |
| day (sidereal) | d | ≡ Time needed for the Earth to rotate once around its axis, determined from successive transits of a very distant astronomical object across an observer's meridian (International Celestial Reference Frame) | ≈ 86 164.1 s |
| decade | dec | ≡ 10 a (see below for definition of year length) | = 10 years |
| fortnight | fn | ≡ 2 wk | = 1 209 600 s |
| helek | ≡ 1/1 080 h | = 3.3 s | |
| Hipparchic cycle | ≡ 4 Callippic cycles - 1 d | = 9.593 424×109 s | |
| hour | h | ≡ 60 min | = 3 600 s |
| jiffy | j | ≡ 1/60 s | = .016 s |
| jiffy (alternate) | ja | ≡ 1/100 s | = 10 ms |
| ke (quarter of an hour) | ≡ ¼ h = 1/96 d | = 60 × 60 / 4 s = 900 s = 60 / 4 min = 15 min | |
| ke (traditional) | ≡ 1/100 d | = 24 × 60 × 60 / 100 s = 864 s = 24 * 60 / 100 min = 14.4 min | |
| lustre; lustrum | ≡ 5 a of 365 d | = 1.5768×108 s | |
| Metonic cycle; enneadecaeteris | ≡ 110 mo (hollow) + 125 mo (full) = 6940 d ≈ 19 a | = 5.996 16×108 s | |
| millennium | ≡ 1 000 a (see below for definition of year length) | = 1000 years | |
| milliday | md | ≡ 1/1 000 d | = 24 × 60 × 60 / 1 000 s = 86.4 s |
| minute | min | ≡ 60 s, due to leap seconds sometimes 59 s or 61 s, | = 60 s |
| moment | ≡ 90 s | = 90 s | |
| month (full) | mo | ≡ 30 d | = 2 592 000 s |
| month (Greg. av.) | mo | Average Gregorian month = 365.2425/12 d = 30.436875 d | ≈ 2.6297×106 s |
| month (hollow) | mo | ≡ 29 d | = 2 505 600 s |
| month (synodic) | mo | Cycle time of moon phases ≈ 29.530589 days (Average) | ≈ 2.551×106 s |
| octaeteris | = 48 mo (full) + 48 mo (hollow) + 3 mo (full) = 8 a of 365.25 d = 2922 d | = 2.524 608×108 s | |
| Planck time | ≡ (Gℏ/c5)½ | ≈ 1.351 211 868×10−43 s | |
| second | s | time of 9 192 631 770 periods of the radiation corresponding to the transition between the 2 hyperfine levels of the ground state of the caesium 133 atom at 0 K (but other seconds are sometimes used in astronomy) | (SI base unit) |
| shake | ≡ 10−8 s | = 10 ns | |
| sigma | ≡ 10−6 s | = 1 μs | |
| Sothic cycle | ≡ 1 461 a of 365 d | = 4.607 4096×1010 s | |
| svedberg | S | ≡ 10−13 s | = 100 fs |
| week | wk | ≡ 7 d | = 168 h = 10 080 min = 604 800 s |
| year (Gregorian) | a, y, or yr | = 365.2425 d average, calculated from common years (365 d) plus leap years (366 d) on most years divisible by 4. See leap year for details. | = 31 556 952 s |
| year (Julian) | a, y, or yr | = 365.25 d average, calculated from common years (365 d) plus one leap year (366 d) every four years | = 31 557 600 s |
| year (sidereal) | a, y, or yr | ≡ time taken for Sun to return to the same position with respect to the stars of the celestial sphere | ≈ 365.256 363 d ≈ 31 558 149.7632 s |
| year (tropical) | a, y, or yr | ≡ Length of time it takes for the Sun to return to the same position in the cycle of seasons | ≈ 365.242 190 d ≈ 31 556 925 s |
| Where UTC is observed, the length of time units longer than 1 s may increase or decrease by 1 s if a leap second occurs during the time interval of interest. | |||
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| hertz (SI unit) | Hz | ≡ Number of cycles per second | = 1 Hz = 1/s |
| revolutions per minute | rpm | ≡ One unit rpm equals one rotation completed around a fixed axis in one minute of time. | ≈ 0.104719755 rad/s |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| foot per hour | fph | ≡ 1 ft/h | ≈ 8.466 667×10−5 m/s |
| foot per minute | fpm | ≡ 1 ft/min | = 5.08×10−3 m/s |
| foot per second | fps | ≡ 1 ft/s | = 3.048×10−1 m/s |
| furlong per fortnight | ≡ furlong/fortnight | ≈ 1.663 095×10−4 m/s | |
| inch per hour | iph | ≡ 1 in/hr | ≈ 7.05 556×10−6 m/s |
| inch per minute | ipm | ≡ 1 in/min | ≈ 4.23 333×10−4 m/s |
| inch per second | ips | ≡ 1 in/s | = 2.54×10−2 m/s |
| kilometre per hour | km/h | ≡ 1 km/h | ≈ 2.777 778×10−1 m/s |
| knot | kn, kt | ≡ 1 NM/h = 1.852 km/h | ≈ 0.514 444 m/s |
| knot (Admiralty) | kn | ≡ 1 NM (Adm)/h = 1.853 184 km/h | = 0.514 773 m/s |
| mach number | M | Ratio of the speed to the speed of sound in the medium. Varies especially with temperature. About 1225 km/h (761 mph) in air at sea level to about 1062 km/h (660 mph) at jet altitudes. Unitless | ≈ 340 to 295 m/s for aircraft |
| metre per second (SI unit) | m/s | ≡ 1 m/s | = 1 m/s |
| mile per hour | mph | ≡ 1 mi/h | = 0.447 04 m/s |
| mile per minute | mpm | ≡ 1 mi/min | = 26.8224 m/s |
| mile per second | mps | ≡ 1 mi/s | = 1 609.344 m/s |
| speed of light in vacuum | c | ≡ 299 792 458 m/s | = 299 792 458 m/s |
| speed of sound in air | s | Varies especially with temperature. About 1225 km/h (761 mph) in air at sea level to about 1062 km/h (660 mph) at jet altitudes. | ≈ 340 to 295 m/s at aircraft altitudes |
A velocity consists of a speed combined with a direction; the speed part of the velocity takes units of speed.
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| cubic foot per minute | CFM | ≡ 1 ft3/min | = 4.719474432×10−4 m3/s |
| cubic foot per second | ft3/s | ≡ 1 ft3/s | = 0.028316846592 m3/s |
| cubic inch per minute | in3/min | ≡ 1 in3/min | = 2.7311773×10−7 m3/s |
| cubic inch per second | in3/s | ≡ 1 in3/s | = 1.6387064×10−5 m3/s |
| cubic metre per second (SI unit) | m3/s | ≡ 1 m3/s | = 1 m3/s |
| gallon (US fluid) per day | GPD | ≡ 1 gal/d | = 4.381263638×10−8 m3/s |
| gallon (US fluid) per hour | GPH | ≡ 1 gal/h | = 1.051503273×10−6 m3/s |
| gallon (US fluid) per minute | GPM | ≡ 1 gal/min | = 6.30901964×10−5 m3/s |
| litre per minute | LPM | ≡ 1 L/min | = 1.6×10−5 m3/s |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| foot per hour per second | fph/s | ≡ 1 ft/(h·s) | ≈ 8.466 667×10−5 m/s2 |
| foot per minute per second | fpm/s | ≡ 1 ft/(min·s) | = 5.08×10−3 m/s2 |
| foot per second squared | fps2 | ≡ 1 ft/s2 | = 3.048×10−1 m/s2 |
| gal; galileo | Gal | ≡ 1 cm/s2 | = 10−2 m/s2 |
| inch per minute per second | ipm/s | ≡ 1 in/(min·s) | ≈ 4.233 333×10−4 m/s2 |
| inch per second squared | ips2 | ≡ 1 in/s2 | = 2.54×10−2 m/s2 |
| knot per second | kn/s | ≡ 1 kn/s | ≈ 5.144 444×10−1 m/s2 |
| metre per second squared (SI unit) | m/s2 | ≡ 1 m/s2 | = 1 m/s2 |
| mile per hour per second | mph/s | ≡ 1 mi/(h·s) | = 4.4704×10−1 m/s2 |
| mile per minute per second | mpm/s | ≡ 1 mi/(min·s) | = 26.8224 m/s2 |
| mile per second squared | mps2 | ≡ 1 mi/s2 | = 1.609 344×103 m/s2 |
| standard gravity | g | ≡ 9.806 65 m/s2 | = 9.806 65 m/s2 |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| atomic unit of force | ≡ me·α2·c2/a0 | ≈ 8.238 722 06×10−8 N | |
| dyne (cgs unit) | dyn | ≡ g·cm/s2 | = 10−5 N |
| kilogram-force; kilopond; grave-force | kgf; kp; Gf | ≡ g × 1 kg | = 9.806 65 N |
| kip; kip-force | kip; kipf; klbf | ≡ g × 1 000 lb | = 4.448 221 615 2605×103 N |
| milligrave-force, gravet-force | mGf; gf | ≡ g × 1 g | = 9.806 65 mN |
| newton (SI unit) | N | A force capable of giving a mass of one kg an acceleration of one metre per second, per second. | = 1 N = 1 kg·m/s2 |
| ounce-force | ozf | ≡ g × 1 oz | = 0.278 013 850 953 7812 N |
| pound-force | lbf | ≡ g × 1 lb | = 4.448 221 615 2605 N |
| poundal | pdl | ≡ 1 lb·ft/s2 | = 0.138 254 954 376 N |
| sthene (mts unit) | sn | ≡ 1 t·m/s2 | = 1×103 N |
| ton-force | tnf | ≡ g × 1 sh tn | = 8.896 443 230 521×103 N |
See also: Conversion between weight (force) and mass
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| atmosphere (standard) | atm | ≡ 101 325 Pa | |
| atmosphere (technical) | at | ≡ 1 kgf/cm2 | = 9.806 65×104 Pa |
| bar | bar | ≡ 105 Pa | |
| barye (cgs unit) | ≡ 1 dyn/cm2 | = 0.1 Pa | |
| centimetre of mercury | cmHg | ≡ 13 595.1 kg/m3 × 1 cm × g | ≈ 1.333 22×103 Pa |
| centimetre of water (4 °C) | cmH2O | ≈ 999.972 kg/m3 × 1 cm × g | ≈ 98.063 8 Pa |
| foot of mercury (conventional) | ftHg | ≡ 13 595.1 kg/m3 × 1 ft × g | ≈ 40.636 66×103 Pa |
| foot of water (39.2 °F) | ftH2O | ≈ 999.972 kg/m3 × 1 ft × g | ≈ 2.988 98×103 Pa |
| inch of mercury (conventional) | inHg | ≡ 13 595.1 kg/m3 × 1 in × g | ≈ 3.386 389×103 Pa |
| inch of water (39.2 °F) | inH2O | ≈ 999.972 kg/m3 × 1 in × g | ≈ 249.082 Pa |
| kilogram-force per square millimetre | kgf/mm2 | ≡ 1 kgf/mm2 | = 9.806 65×106 Pa |
| kip per square inch | ksi | ≡ 1 kipf/sq in | ≈ 6.894 757×106 Pa |
| micron (micrometre) of mercury | μmHg | ≡ 13 595.1 kg/m3 × 1 μm × g ≈ 0.001 torr | ≈ 0.133 322 4 Pa |
| millimetre of mercury | mmHg | ≡ 13 595.1 kg/m3 × 1 mm × g ≈ 1 torr | ≈ 133.3224 Pa |
| millimetre of water (3.98 °C) | mmH2O | ≈ 999.972 kg/m3 × 1 mm × g = 0.999 972 kgf/m2 | = 9.806 38 Pa |
| pascal (SI unit) | Pa | ≡ N/m2 = kg/(m·s2) | = 1 Pa |
| pièze (mts unit) | pz | ≡ 1 000 kg/m·s2 | = 1×103 Pa = 1 kPa |
| pound per square foot | psf | ≡ 1 lbf/ft2 | ≈ 47.880 26 Pa |
| pound per square inch | psi | ≡ 1 lbf/in2 | ≈ 6.894 757×103 Pa |
| poundal per square foot | pdl/sq ft | ≡ 1 pdl/sq ft | ≈ 1.488 164 Pa |
| short ton per square foot | ≡ 1 sh tn × g / 1 sq ft | ≈ 95.760 518×103 Pa | |
| torr | torr | ≡ 101 325/760 Pa | ≈ 133.322 4 Pa |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| foot-pound force | ft lbf | ≡ g × 1 lb × 1 ft | = 1.355 817 948 331 4004 N·m |
| foot-poundal | ft pdl | ≡ 1 lb·ft2/s2 | = 4.214 011 009 380 48×10−2 N·m |
| inch-pound force | in lbf | ≡ g × 1 lb × 1 in | = 0.112 984 829 027 6167 N·m |
| metre kilogram | m kg | ≡ N × m / g | ≈ 0.101 971 621 N·m |
| Newton metre (SI unit) | N·m | ≡ N × m = kg·m2/s2 | = 1 N·m |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| barrel of oil equivalent | bboe | ≈ 5.8×106 BTU59 °F | ≈ 6.12×109 J |
| British thermal unit (ISO) | BTUISO | ≡ 1.0545×103 J | = 1.0545×103 J |
| British thermal unit (International Table) | BTUIT | = 1.055 055 852 62×103 J | |
| British thermal unit (mean) | BTUmean | ≈ 1.055 87×103 J | |
| British thermal unit (thermochemical) | BTUth | ≈ 1.054 350×103 J | |
| British thermal unit (39 °F) | BTU39 °F | ≈ 1.059 67×103 J | |
| British thermal unit (59 °F) | BTU59 °F | ≡ 1.054 804×103 J | = 1.054 804×103 J |
| British thermal unit (60 °F) | BTU60 °F | ≈ 1.054 68×103 J | |
| British thermal unit (63 °F) | BTU63 °F | ≈ 1.0546×103 J | |
| calorie (International Table) | calIT | ≡ 4.1868 J | = 4.1868 J |
| calorie (mean) | calmean | 1⁄100 of the energy required to warm one gram of air-free water from 0 °C to 100 °C @ 1 atm | ≈ 4.190 02 J |
| calorie (thermochemical) | calth | ≡ 4.184 J | = 4.184 J |
| calorie (3.98 °C) | cal3.98 °C | ≈ 4.2045 J | |
| calorie (15 °C) | cal15 °C | ≡ 4.1855 J | = 4.1855 J |
| calorie (20 °C) | cal20 °C | ≈ 4.1819 J | |
| Celsius heat unit (International Table) | CHUIT | ≡ 1 BTUIT × 1 K/°R | = 1.899 100 534 716×103 J |
| cubic centimetre of atmosphere; standard cubic centimetre | cc atm; scc | ≡ 1 atm × 1 cm3 | = 0.101 325 J |
| cubic foot of atmosphere; standard cubic foot | cu ft atm; scf | ≡ 1 atm × 1 ft3 | = 2.869 204 480 9344×103 J |
| cubic foot of natural gas | ≡ 1 000 BTUIT | = 1.055 055 852 62×106 J | |
| cubic yard of atmosphere; standard cubic yard | cu yd atm; scy | ≡ 1 atm × 1 yd3 | = 77.468 520 985 2288×103 J |
| electronvolt | eV | ≡ e × 1 V | ≈ 1.602 177 33×10−19 ± 4.9×10−26 J |
| erg (cgs unit) | erg | ≡ 1 g·cm2/s2 | = 10−7 J |
| foot-pound force | ft lbf | ≡ g × 1 lb × 1 ft | = 1.355 817 948 331 4004 J |
| foot-poundal | ft pdl | ≡ 1 lb·ft2/s2 | = 4.214 011 009 380 48×10−2 J |
| gallon-atmosphere (imperial) | imp gal atm | ≡ 1 atm × 1 gal (imp) | = 460.632 569 25 J |
| gallon-atmosphere (US) | US gal atm | ≡ 1 atm × 1 gal (US) | = 383.556 849 0138 J |
| hartree, atomic unit of energy | Eh | ≡ me·α2·c2 (= 2 Ry) | ≈ 4.359 744×10−18 J |
| horsepower-hour | hp·h | ≡ 1 hp × 1 h | = 2.684 519 537 696 172 792×106 J |
| inch-pound force | in lbf | ≡ g × 1 lb × 1 in | = 0.112 984 829 027 6167 J |
| joule (SI unit) | J | The work done when a force of one newton moves the point of its application a distance of one metre in the direction of the force. | = 1 J = 1 m·N = 1 kg·m2/s2 = 1 C·V = 1 W·s |
| kilocalorie; large calorie | kcal; Cal | ≡ 1 000 calIT | = 4.1868×103 J |
| kilowatt-hour; Board of Trade Unit | kW·h; B.O.T.U. | ≡ 1 kW × 1 h | = 3.6×106 J |
| litre-atmosphere | l atm; sl | ≡ 1 atm × 1 L | = 101.325 J |
| quad | ≡ 1015 BTUIT | = 1.055 055 852 62×1018 J | |
| rydberg | Ry | ≡ R∞·ℎ·c | ≈ 2.179 872×10−18 J |
| therm (E.C.) | ≡ 100 000 BTUIT | = 105.505 585 262×106 J | |
| therm (US) | ≡ 100 000 BTU59 °F | = 105.4804×106 J | |
| thermie | th | ≡ 1 McalIT | = 4.1868×106 J |
| ton of coal equivalent | TCE | ≡ 7 Gcalth | = 29.3076×109 J |
| ton of oil equivalent | TOE | ≡ 10 Gcalth | = 41.868×109 J |
| ton of TNT | tTNT | ≡ 1 Gcalth | = 4.184×109 J |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| atmosphere-cubic centimetre per minute | atm ccm | ≡ 1 atm × 1 cm3/min | = 1.688 75×10−3 W |
| atmosphere-cubic centimetre per second | atm ccs | ≡ 1 atm × 1 cm3/s | = 0.101 325 W |
| atmosphere-cubic foot per hour | atm cfh | ≡ 1 atm × 1 cu ft/h | = 0.797 001 244 704 W |
| atmosphere-cubic foot per minute | atm·cfm | ≡ 1 atm × 1 cu ft/min | = 47.820 074 682 24 W |
| atmosphere-cubic foot per second | atm cfs | ≡ 1 atm × 1 cu ft/s | = 2.869 204 480 9344×103 W |
| BTU (International Table) per hour | BTUIT/h | ≡ 1 BTUIT/h | ≈ 0.293 071 W |
| BTU (International Table) per minute | BTUIT/min | ≡ 1 BTUIT/min | ≈ 17.584 264 W |
| BTU (International Table) per second | BTUIT/s | ≡ 1 BTUIT/s | = 1.055 055 852 62×103 W |
| calorie (International Table) per second | calIT/s | ≡ 1 calIT/s | = 4.1868 W |
| erg per second | erg/s | ≡ 1 erg/s | = 10−7 W |
| foot-pound-force per hour | ft lbf/h | ≡ 1 ft lbf/h | ≈ 3.766 161×10−4 W |
| foot-pound-force per minute | ft lbf/min | ≡ 1 ft lbf/min | = 2.259 696 580 552 334×10−2 W |
| foot-pound-force per second | ft lbf/s | ≡ 1 ft lbf/s | = 1.355 817 948 331 4004 W |
| horsepower (boiler) | bhp | ≈ 34.5 lb/h × 970.3 BTUIT/lb | ≈ 9.810 657×103 W |
| horsepower (European electrical) | hp | ≡ 75 kp·m/s | = 736 W |
| horsepower (imperial electrical) | hp | ≡ 746 W | = 746 W |
| horsepower (imperial mechanical) | hp | ≡ 550 ft lbf/s | = 745.699 871 582 270 22 W |
| horsepower (metric) | hp | ≡ 75 m kgf/s | = 735.498 75 W |
| litre-atmosphere per minute | L·atm/min | ≡ 1 atm × 1 L/min | = 1.688 75 W |
| litre-atmosphere per second | L·atm/s | ≡ 1 atm × 1 L/s | = 101.325 W |
| lusec | lusec | ≡ 1 L·µmHg/s | ≈ 1.333×10−4 W |
| poncelet | p | ≡ 100 m kgf/s | = 980.665 W |
| square foot equivalent direct radiation | sq ft EDR | ≡ 240 BTUIT/h | ≈ 70.337 057 W |
| ton of air conditioning | ≡ 1 t ice melted / 24 h | ≈ 3 504 W | |
| ton of refrigeration (imperial) | ≡ 1 BTUIT × 1 lng tn/lb ÷ 10 min/s | ≈ 3.938 875×103 W | |
| ton of refrigeration (IT) | ≡ 1 BTUIT × 1 sh tn/lb ÷ 10 min/s | ≈ 3.516 853×103 W | |
| watt (SI unit) | W | The power which in one second of time gives rise to one joule of energy. | = 1 W = 1 J/s = 1 N·m/s = 1 kg·m2/s3 |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| atomic unit of action | au | ≡ ℏ ≡ ℎ/2π | ≈ 1.054 571 68×10−34 J·s |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| pascal second (SI unit) | Pa·s | ≡ N·s/m2, kg/(m·s) | = 1 Pa·s |
| poise (cgs unit) | P | ≡ 1 barye·s | = 0.1 Pa·s |
| pound per foot hour | lb/(ft·h) | ≡ 1 lb/(ft·h) | ≈ 4.133 789×10−4 Pa·s |
| pound per foot second | lb/(ft·s) | ≡ 1 lb/(ft·s) | ≈ 1.488164 Pa·s |
| pound-force second per square foot | lbf·s/ft2 | ≡ 1 lbf·s/ft2 | ≈ 47.88026 Pa·s |
| pound-force second per square inch | lbf·s/in2 | ≡ 1 lbf·s/in2 | ≈ 6,894.757 Pa·s |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| square foot per second | ft2/s | ≡ 1 ft2/s | = 0.09290304 m2/s |
| square metre per second (SI unit) | m2/s | ≡ 1 m2/s | = 1 m2/s |
| stokes (cgs unit) | St | ≡ 10−4 m2/s | = 10−4 m2/s |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| ampere (SI base unit) | A | ≡ The constant current needed to produce a force of 2 ×10−7 newton per metre between two straight parallel conductors of infinite length and negligible circular cross-section placed one metre apart in a vacuum. | = 1 A |
| electromagnetic unit; abampere (cgs unit) | abamp | ≡ 10 A | = 10 A |
| esu per second; statampere (cgs unit) | esu/s | ≡ (0.1 A·m/s) / c | ≈ 3.335641×10−10 A |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| abcoulomb; electromagnetic unit (cgs unit) | abC; emu | ≡ 10 C | = 10 C |
| atomic unit of charge | au | ≡ e | ≈ 1.602 176 462×10−19 C |
| coulomb (SI unit) | C | ≡ The amount of electricity carried in one second of time by one ampere of current. | = 1 C = 1 A·s |
| faraday | F | ≡ 1 mol × NA·e | ≈ 96 485.3383 C |
| statcoulomb; franklin; electrostatic unit (cgs unit) | statC; Fr; esu | ≡ (0.1 A·m) / c | ≈ 3.335 641×10−10 C |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| atomic unit of electric dipole moment | ea0 | ≈ 8.478 352 81×10−30 C·m | |
| coulomb meter | C·m | = 1 C · 1 m | |
| debye | D | = 10−10 esu·Å | = 3.33564095×10−30 C·m |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| abvolt (cgs unit) | abV | ≡ 1×10−8 V | = 1×10−8 V |
| statvolt (cgs unit) | statV | ≡ c· (1 μJ/A·m) | = 299.792 458 V |
| volt (SI unit) | V | The difference in electric potential across two points along a conducting wire carrying one ampere of constant current when the power dissipated between the points equals one watt. | = 1 V = 1 W/A = 1 kg·m2/(A·s3) |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| ohm (SI unit) | Ω | The resistance between two points in a conductor when one volt of electric potential difference, applied to these points, produces one ampere of current in the conductor. | = 1 Ω = 1 V/A = 1 kg·m2/(A2·s3) |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| farad (SI unit) | F | The capacitance between two parallel plates that results in one volt of potential difference when charged by one coulomb of electricity. | = 1 F = 1 C/V = 1 A2·s4/(kg·m2) |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| maxwell (CGS unit) | Mx | ≡ 10−8 Wb | = 1×10−8 Wb |
| weber (SI unit) | Wb | Magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second. | = 1 Wb = 1 V·s = 1 kg·m2/(A·s2) |
What physicists call Magnetic field is called Magnetic flux density by electrical engineers and magnetic induction by applied mathematicians and electrical engineers.
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| gauss (CGS unit) | G | ≡ Mx/cm2 = 10−4 T | = 1×10−4 T |
| tesla (SI unit) | T | ≡ Wb/m2 | = 1 T = 1 Wb/m2 = 1 kg/(A·s2) |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| henry (SI unit) | H | The inductance of a closed circuit that produces one volt of electromotive force when the current in the circuit varies at a uniform rate of one ampere per second. | = 1 H = 1 Wb/A = 1 kg·m2/(A·s)2 |
| Name of unit | Symbol | Definition | Conversion to kelvin |
|---|---|---|---|
| degree Celsius | °C | °C ≡ K − 273.15 | [K] ≡ [°C] + 273.15 |
| degree Delisle | °De | [K] = 373.15 − [°De] × 2/3 | |
| degree Fahrenheit | °F | °F ≡ °C × 9/5 + 32 | [K] ≡ ([°F] + 459.67) × 5/9 |
| degree Newton | °N | [K] = [°N] × 100/33 + 273.15 | |
| degree Rankine | °R; | °R ≡ K × 9/5 | [K] ≡ [°R] × 5/9 |
| degree Réaumur | °Ré | [K] = [°Ré] × 5/4 + 273.15 | |
| degree Rømer | °Rø | [K] = ([°Rø] − 7.5) × 40/21 + 273.15 | |
| kelvin (SI base unit) | K | ≡ 1/273.16 of the thermodynamic temperature of the triple point of water. | ≡ 1 K |
| Name of unit | Symbol | Definition | Relation to SI units | Relation to bits |
|---|---|---|---|---|
| SI unit | J/K | ≡ J/K | = 1 J/K | |
| nat; nip; nepit | nat | ≡ kB | = 1.380 650 5(23)×10−23 J/K | |
| bit; shannon | bit; b; Sh | ≡ ln(2) × kB | = 9.569 940 (16)×10−24 J/K | = 1 bit |
| ban; hartley | ban; Hart | ≡ ln(10) × kB | = 3.179 065 3(53)×10−23 J/K | |
| nibble | ≡ 4 bits | = 3.827 976 0(64)×10−23 J/K | = 22 bit | |
| byte | B | ≡ 8 bits | = 7.655 952 (13)×10−23 J/K | = 23 bit |
| kilobyte (decimal) | kB | ≡ 1 000 B | = 7.655 952 (13)×10−20 J/K | = 8×103 bit = 8000 bit |
| kilobyte (kibibyte) | KB; KiB | ≡ 1 024 B | = 7.839 695 (13)×10−20 J/K | = 213 bit = 8192 bit |
Often, information entropy is measured in shannons, whereas the (discrete) storage space of digital devices is measured in bits. Thus, uncompressed redundant data occupy more than one bit of storage per shannon of information entropy. The multiples of a bit listed above are usually used with this meaning. Other times the bit is used as a measure of information entropy and is thus a synonym of shannon.
The candela is the preferred nomenclature for the SI unit.
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| candela (SI base unit); candle | cd | The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. | = 1 cd |
| candlepower (new) | cp | ≡ cd The use of candlepower as a unit is discouraged due to its ambiguity. | = 1 cd |
| candlepower (old, pre-1948) | cp | Varies and is poorly reproducible. Approximately 0.981 cd. | ≈ 0.981 cd |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| candela per square foot | cd/ft2 | ≡ cd/ft2 | ≈ 10.763910417 cd/m2 |
| candela per square inch | cd/in2 | ≡ cd/in2 | ≈ 1,550.0031 cd/m2 |
| candela per square metre (SI unit); nit (deprecated) | cd/m2 | ≡ cd/m2 | = 1 cd/m2 |
| footlambert | fL | ≡ (1/π) cd/ft2 | ≈ 3.4262590996 cd/m2 |
| lambert | L | ≡ (104/π) cd/m2 | ≈ 3,183.0988618 cd/m2 |
| stilb (CGS unit) | sb | ≡ 104 cd/m2 | ≈ 1×104 cd/m2 |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| lumen (SI unit) | lm | ≡ cd·sr | = 1 lm = 1 cd·sr |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| footcandle; lumen per square foot | fc | ≡ lm/ft2 | = 10.763910417 lx |
| lumen per square inch | lm/in2 | ≡ lm/in2 | ≈ 1,550.0031 lx |
| lux (SI unit) | lx | ≡ lm/m2 | = 1 lx = 1 lm/m2 |
| phot (CGS unit) | ph | ≡ lm/cm2 | = 1×104 lx |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| becquerel (SI unit) | Bq | ≡ Number of disintegrations per second | = 1 Bq = 1/s |
| curie | Ci | ≡ 3.7×1010 Bq | = 3.7×1010 Bq |
| rutherford (H) | rd | ≡ 1 MBq | = 1×106 Bq |
Please note that although becquerel (Bq) and hertz (Hz) both ultimately refer to the same SI base unit (s−1), Hz is used only for periodic phenomena, and Bq is only used for stochastic processes associated with radioactivity.
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| roentgen | R | 1 R ≡ 2.58×10−4 C/kg | = 2.58×10−4 C/kg |
The roentgen is not a SI unit and the NIST strongly discourages its continued use.
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| gray (SI unit) | Gy | ≡ 1 J/kg = 1 m2/s2 | = 1 Gy |
| rad | rad | ≡ 0.01 Gy | = 0.01 Gy |
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| Röntgen equivalent man | rem | ≡ 0.01 Sv | = 0.01 Sv |
| sievert (SI unit) | Sv | ≡ 1 J/kg | = 1 Sv |
Although the definitions for sievert (Sv) and gray (Gy) would seem to indicate that they measure the same quantities, this is not the case. The effect of receiving a certain dose of radiation (given as Gy) is variable and depends on many factors, thus a new unit was needed to denote the biological effectiveness of that dose on the body; this is known as the equivalent dose and is shown in Sv. The general relationship between absorbed dose and equivalent dose can be represented as
H = Q · D
where H is the equivalent dose, D is the absorbed dose, and Q is a dimensionless quality factor. Thus, for any quantity of D measured in Gy, the numerical value for H measured in Sv may be different.
b c de f g h i j lm n o p q r st v w
types of wood | units of measurement
abalone - Farbiges Perlmutt
action - Saitenlage
adjusting nut - Einstellmutter
allen key - Innensechskant (Inbus) Schlüssel
amplifier - Verstärker
attack - Anklingzeit
AWG - American wire gauge - Drahtmaß
ball end - Befestigungsröllchen am Saitenende
ball bearing - Kugellager
bar magnet - Stabmagnet, Rundmagnet
belt sander - Bandschleifer
bending iron - Biegeeisen
binding - Randeinfassung mit Zierleisten
blank - Brett
bobbin - Spule, Spulenkörper
body - Korpus
boiled linseed oil - Leinölfirnis
bolt - Zylinderschraube
boost - Anhebung (Elektronik)
bone - Knochen
brace - Verstrebungsleiste
brass - Messing
bridge - Steg
brush - Pinsel
buffing - Hochglanzpolitur per Hand oder Schwabbelscheibe
100% burn in - ansatzlos burnisher - Abziehstahl
buzz - klirren, summen
caliper - Tastlehre, Schiebelehre
capacitor - Kondensator
carbon fiber - Kohlefaser
case - Koffer
cavity - Ausnehmung, Ausfräsung
chisel - Stecheisen, Stechbeitel
clamp - Zwinge
compound radius - Der Griffbrettradius ist am Sattel und am Griffbrettende
unterschiedlich.
control - Einstellregler
coping saw - Laubsäge
copper - Kupfer
cord - (Gitarren)kabel
curved fingerboard - Gewölbtes Griffbrett
cutaway - Korpusausnehmung
cutter bit - Fräser
dead spots - Punkte auf dem Griffbrett mit verschlechtertem Sustain. Hals-
und Saitenresonanz stimmen überein.
die - Gewinde-Schneideisen
dots - Orientierungspunkte auf dem Griffbrett
double-stick tape - Doppelseitig klebendes Band
dovetail - Schwalbenschwanz
DPDT (double pole double throw) - zweipoliger Umschalter
drill bit - Bohrer
end grain - Hirnholz
feedback - Rückkopplung
fingerboard - Griffbrett
flat magnet - Flachmagnet
flatsawn - “liegende Jahresringe”
flat wound string - Flachdrahtumwickelte Saite
flush-trimming cutter bit - Bündigfräser
foot - Fuß
french polishing - Schellackpolitur
fret - Bund
fretfile - Bundfeile
fretboard - Griffbrett
fretless - Bundlos
fretwire - Bunddraht
gauge - Lehre
glue - Leim, Kleber
ground - Schaltungsmasse (Elektronik)
guitar scale - Mensur
hardware - Montageteil
headstock - Kopfplatte
headstock veneer - Kopfplattenfurnier
heel - Absatz, Fuß beim Gitarrenhals
humbucker - Brummunterdrückende Zusammenschaltung zweier Singlecoils
inches - Zoll
inlay - Einlage
jig - Hilfsvorrichtung
jigsaw - (Elektrische) Stichsäge
lacquer - Lack (meist Nitrozellulose)
lever-action switch - Hebelschalter
lining - Randverstärkung
linseed oil - Leinöl
marquetry - Einlegearbeit
master volume - Gesamtlautstärkeregler
mild-steel - Weichstahl
mineral spirits - Lösungsmittel, Terpentinersatz
mother of pearl - weißes Perlmutt
naphta - Waschbenzin
neck - Hals
nut - Sattel, Schraubmutter
output jack - Ausgangsbuchse
pearl - Perlmutt
peghead - Kopfplatte
peghead veneer - Kopfplattenfurnier
pickguard - Schlagbrett
pickup (PU) - Tonabnehmer (TA)
pin-router - Oberarmfräse
plane - Hobel
pole - Pol, Ebene bei Schaltern
potentiometer - Potentiometer
pumice - Bimsstein
purfling - Zierrandeinlage
quartersawn - “stehende Jahresringe”
radiused fingerboard - Gewölbtes Griffbrett
rasp - Raspel
reamer - Reibahle
refret - Neu-Bundierung
release - Abklingzeit
resistor - Widerstand (Elektronik)
rod - Stab, Stange
rounding-over bit - Kantenabrundungsfräser
round wound string - Runddrahtumwickelte Saite
router - Handoberfräse
router bit - Fräser
ruler - Lineal
saddle - Stegeinlage
scale length - Mensur
scraper - Ziehklinge
screw - Holzschraube
shaper - Tischfräse
shellac - Schellack
shield - Abschirmung
single-coil - Einzelspule
soundboard - Gitarrendecke
spray gun - Spritzpistole
stain - Beize
straight edge - Richtscheit
strap button - Gurthalteknopf
string gauge - Saitenstärke
string spacing - Saitenabstand
strings - Saiten
sunburst - spezielle Lackierungsart
super glue - Superkleber
surface-trim cutter bit - Spezieller Oberflächenfräser
sustain - Ausklingzeit
switch - Schalter
tailpiece - Saitenhalter
TCT (Tungsten Carbide Tipped) - Hartmetallwerkzeugspitze
template - Schablone
tension - Zug, Dehnung (Mechanik)
thread - Gewinde
toggle switch - Kippschalter
tone - Klang
transducer - Übertrager
truss rod - Halseinstellstab
tuner - Stimm-Mechanik, Stimmgerät
tuning machine - Stimm-Mechanik
turpentine - Aus natürlichem Harz gewonnenes Terpentin
twist drill - Metallbohrer
varnish - Firnis, Öllack, Geigenlack
veneer - Furnier
vintage - Antiquität
vise - Schraubstock
volume - Lautstärke
washer - Beilagscheibe
wax - Wachs
wire - Draht
wrench - Schraubenschlüssel
alder - Erle
ash - Esche
basswood - Linde
birch - Birke
birds eye maple - Vogelaugen-Ahorn
cedar- Zeder
cherry - Kirsche
curly maple - Wölkchen-Ahorn
cypress - Zypresse
ebony - Ebenholz
fir - Tanne
flamed maple - Riegel-Ahorn
hard rock maple - Zuckerahorn
mahogany - Mahagoni
maple - Ahorn
oak - Eiche
pear - Birne
pine - Kiefer
plywood - Sperrholz
rosewood - Palisander
spruce - Fichte
swamp ash - Sumpfesche
walnut - Walnuß
Length
1 inch = 1 Zoll =1" = 25.4mm
1/2" = 12.7000mm
1/4" = 6.3500mm
1/8" = 3.1750mm
1/16" = 1.5875mm
1/32" = 0.7938mm
1/64" = 0.3969mm
1 foot = 12 inches = 30.48cm
Weight
1 ounce = 1 Unze = 28.3495 g
1 pound = 1 Pfund =
16 ounces = 0.4536 kg
Volume (fluids)
1 pint = 16 ounces = 0.4732 l
1 quart = 2 pints = 0.9464 l
1 gallon = 4 quarts = 3.7854 l
Pressure
1 psi (pounds per square inch) = approx. 0.07 bar
14 psi = approx. 1 bar = approx. 1 kp/cm2 (the pressure of a 10-
meter- or approx. 30-feet-high water column)
Volume
1 cubic inch = 16.387 cubic centimeters
1 cubic foot = 0.028 cubic meters
Temperature
Celsius = (Fahrenheit - 32) / 1.8
150°F = 65.5°C
Fahrenheit = Celsius x 1.8 + 32
20°C = 68°F