namespace: http://www.xml-cml.org/units/siUnits
id | title | symbol | unitType | multSI | SI.id | description | unitType description |
---|---|---|---|---|---|---|---|
a.m-1 | ampere per metre | A.m-1 | magnetic_field_strength | 1.0 | a.m-1 | not yet added | Magnetic field strength |
a.m-2 | ampere per square metre | A.m-2 | electric_current_density | 1.0 | a.m-2 | not yet added | electric current density |
ampere | ampere | A | current | 1.0 | ampere | This is equivalent to setting the permeability of vacuum to pi*4E-7 Hm^-1. Prior to 1948, the International Ampere (equal to 0.99985 A) was used; it was defined in terms of the electrolytic deposition rate of silver. | Electrical current |
becquerel | Becquerel | Bq | radioactivity | 1.0 | becquerel | This, therefore, has the same dimensionality as the hertz (s^-1, reciprocal time) - a frequency, in other words. The reason for having a specific unit for radioactivity is slightly unusual; it was specifically introduced because of the dangers to human health which might arise from mistakes involving the units reciprocal second. Using the becquerel unit, a more active (and so, all the other things fixed, more dangerous) source has a higher number. Using 1/s or s as a second instead may lead to confusion. | Radioactivity |
c.kg-1 | coulomb per kilogram | C.kg-1 | exposure | 1.0 | c.kg-1 | not yet added | exposure (X and gamma rays) |
c.m-3 | coulomb per cubic metre | C.m-3 | electric_charge_density | 1.0 | c.m-3 | not yet added | electric charge density |
candela | candela | cd | luminous_intensity | 1.0 | candela | This is based on an older unit, the candlepower, which was referenced to the luminous intensity of a "standard candle" of known composition. The frequency chosen is in the visible spectrum near green, which is within the range where the human eye is most sensitive. | Luminous intensity |
cd.m-2 | candela per square metre | cd.m-2 | luminance | 1.0 | cd.m-2 | not yet added | Luminance |
coulomb | Coulomb | C | electric_charge | 1.0 | coulomb | Also the unit of electric flux. The Coulomb could, in principle, be defined in terms of the elementary charge of the electron and the Josephson and von Klitzing constants; in this case, the kilogram would become a derived rather than fundamental unit. | Electric charge |
f.m-1 | farad per metre | F.m-1 | permittivity | 1.0 | f.m-1 | not yet added | Permittivity |
farad | Farad | F | electric_capacitance | 1.0 | farad | Capacitance is a measure of the total amount of electric charge stored for a given electric potential. The farad is a very large unit; typical capacitors are in the microfarad to picofarad range. Although the farad is named after Michael Faraday, it should not be confused with the Faraday - an older unit of capacitance. | Electric capacitance |
gray | Gray | Gy | radioactive_absorbed_dose | 1.0 | gray | Note that these are the same units as the sievert. To avoid any risk of confusion between the absorbed dose and the equivalent dose, one must use the corresponding special units, namely the gray instead of the joule per kilogram for absorbed dose and the sievert instead of the joule per kilogram for the dose equivalent. | absorbed dose (of ionising radiation) |
gy.s-1 | gray per second | Gy.s-1 | absorbed_dose_rate | 1.0 | gy.s-1 | not yet added | absorbed dose rate |
h.m-1 | henry per metre | H.m-1 | permeability | 1.0 | h.m-1 | not yet added | Permeability (electromagnetism) |
henry | Henry | H | magnetic_inductance | 1.0 | henry | Inductance is a measure of how much magnetic flux is produced for a given circuit. | Inductance |
hertz | Hertz | Hz | frequency | 1.0 | hertz | Periodically varying angles are typically not expressed in Hz, but instead in an appropriate angular unit (such as radians per second). | Frequency |
j.k-1 | joule per kelvin | J.K-1 | heat_capacity | 1.0 | j.k-1 | not yet added | Entropy, Heat Capacity |
j.k-1.kg-1 | joule per kilogram kelvin | J.K-1.kg-1 | specific_heat_capacity | 1.0 | j.k-1.kg-1 | not yet added | Specific heat capacity |
j.k-1.mol-1 | joule per kelvin mole | J.K-1.mol-1 | molar_heat_capacity | 1.0 | j.k-1.mol-1 | not yet added | molar heat capacity |
j.kg-1 | joule per kilogram | J.kg-1 | specific_energy | 1.0 | j.kg-1 | not yet added | specific energy |
j.m-1 | joule per metre | J.m-1 | energy_length_gradient | 1.0 | j.m-1 | Although formally identical to force, many authors report energy gradients as energy per unit length and this unitType preserves the dimensional representation. | energy_length_gradient |
j.m-3 | joule per cubic metre | J.m-3 | energy_density | 1.0 | j.m-3 | not yet added | energy density |
j.mol-1 | joule per mole | J.mol-1 | molar_energy | 1.0 | j.mol-1 | not yet added | molar energy |
joule | Joule | J | energy | 1.0 | joule | This is dimensionally, but not semantically, equivalent to the newton metre, which is typically used as a unit of torque. It is also, significantly, the work required to move an electric charge of one coulomb through an electric potential difference of one volt. | energy |
k | kelvin | K | temperature | 1.0 | k | A temperature in Kelvin is measured with respect to absolute zero - where, except for zero-point motion, molecular motion stops. The unit is named after William Thomson, first Baron Kelvin, a Scottish physicist and engineer. | Temperature |
katal | Katal | kat | catalytic_activity | 1.0 | katal | The katal is not used to express the rate of a reaction; that is expressed in moles per second. Rather, it is used to express catalytic activity which is a property of the catalyst. The katal is invariant of the measurement procedure, but the numerical quantity value is not and depends on the experimental conditions. Therefore, in order to define the quantity of a catalyst, the rate of conversion of a defined chemical reaction has to be specified, preferably of the first order, under strictly controlled conditions. | Catalytic activity |
kg | kilogram | kg | mass | 1.0 | kg | It is the only SI base unit that employs a prefix, and the only SI unit that is still defined in relation to an artifact (a platinum-iridium mass) rather than to a fundamental physical property. | Mass |
kg-1.m3 | cubic metre per kilogram | kg-1.m3 | specific_volume | 1.0 | kg-1.m3 | not yet added | specific volume |
kg.m-3 | Kilogram per cubic metre | kg.m-3 | mass_density | 1.0 | kg.m-3 | not yet added | Density |
m | metre | m | length | 1.0 | m | The modern metre dates from 1791, when it was defined one ten-millionth of the length of the earth's meridian along a quadrant; it became France's official unit of length in 1793. Until 1960, the metre (like the kilogram) was defined by a prototype - in this case, a platinum-iridium bar; in 1960, the SI defined the metre as 1650763.73 wavelengths of the orange-red emission line (the 2p10 - 5d5 transition) in the EM spectrum of Krypton-86 in vacuum. Since 1983, the present definition has been used. | Length |
m-1 | reciprocal metre | m-1 | wavenumber | 1.0 | m-1 | not yet added | Wavenumber |
m-3.mol | mole per cubic metre | m-3.mol | amount_concentration | 1.0 | m-3.mol | not yet added | amount (-of-substance) concentration |
m.s-1 | Metre per second | m.s-1 | velocity | 1.0 | m.s-1 | not yet added | Velocity |
m.s-2 | Metre per second squared | m.s-2 | acceleration | 1.0 | m.s-2 | not yet added | Acceleration |
m2 | Square metre | m2 | area | 1.0 | m2 | not yet added | Area |
m2.s-1 | square metre per second | m2.s-1 | kinematic_viscosity | 1.0 | m2.s-1 | not yet added | Diffusion coefficient, kinematic viscosity |
m3 | Cubic metre | m3 | volume | 1.0 | m3 | not yet added | Volume |
m3.mol-1 | cubic metre per mole | m3.mol-1 | molar_volume | 1.0 | m3.mol-1 | not yet added | molar volume |
mol | mole | mol | amount | 1.0 | mol | The number of atoms in 12 grams of carbon 12 is commonly known as Avogadro's number; it is approximately 6.0221415E23. Prior to 1959, IUPAP and IUPAC defined the mole in terms of oxygen (though the definitions were slightly different from each other); in 1959/1960, the two organizations unified on the present definition. | Amount of substance |
molality | Molality | _i_m__i_ | molality | 1.0 | molality | not yet added | Concentration (moles of substance per mass of solution) |
molarity | Molarity | _i_M__i_ | molarity | 1.0 | molarity | not yet added | Concentration (moles of substance per volume of solution) |
n.m | newton metre | N.m | torque | 1.0 | n.m | not yet added | Torque, moment of force |
n.m-1 | newton per metre | N.m-1 = J.m-2 | surface_tension | 1.0 | n.m-1 | not yet added | Surface tension |
n.m.s | newton metre second | N.m.s | angular_momentum | 1.0 | n.m.s | not yet added | Angular momentum |
n.s | newton second | N.s | momentum | 1.0 | n.s | not yet added | Momentum |
newton | Newton | N | force | 1.0 | newton | Named after Sir Isaac Newton, the Newton was adopted as the name for the MKS (direct predecessor of the SI) unit of force in 1948. A small apple, fittingly, exerts a gravitational force of about 1N on Earth. | Force |
ohm | Ohm | [Omega] | electric_resistance | 1.0 | ohm | Named after Georg Ohm, the German physicist who discovered Ohm's Law; since 1990, the unit has been internationally maintained using the Quantum Hall Effect and a conventional value for the von Klitzing constant. | Resistance, reactance, impedance |
pa.s | Pascal second | Pa.s = N.s.m-2 | dynamic_viscosity | 1.0 | pa.s | not yet added | Dynamic Viscosity |
pascal | Pascal | Pa | pressure | 1.0 | pascal | The pascal, named after Blaise Pascal, is also used to measure stress, Young's modulus, and tensile strength. For atmospheric pressures, however, it is commonly regarded as an inconveniently small unit. | Pressure |
rad.s-1 | radian per second | rad.s-1 | angular_velocity | 1.0 | rad.s-1 | not yet added | Angular velocity |
radian | null | rad | angle | 1.0 | radian | The radian is therefore formally dimensionless, as it is a ratio of two lengths. There are 2*pi radians in a complete circle. | angle |
s | second | s | time | 1.0 | s | The second has had many definitions throughout history; originally, it was one sixtieth of one twenty-fourth of a solar day (the factor of sixty coming from Babylonian counting and the factor of 24 from Ancient Egypt). The present definition dates from the Thirteenth General Conference on Weights and Measures, which took place in 1967. | Time |
s.m-1 | siemens per metre | S.m-1 | electrical_conductivity | 1.0 | s.m-1 | not yet added | Electrical conductivity |
s.m2.mol-1 | siemens square metre per mole | S.m2.mol-1 | molar_conductivity | 1.0 | s.m2.mol-1 | not yet added | molar conductivity |
siemens | Siemens | S | electric_conductance | 1.0 | siemens | This is equivalent to the obsolete "mho" unit (derived from spelling "ohm" backwards and written with an upside-down capital omega). | Electric conductance |
sievert | Sievert | Sv | radioactive_equivalent_dose | 1.0 | sievert | The sievert attempts to reflect the biological effects of radiation as opposed to the physical aspects, which are characterised by the absorbed dose, measured in grays. Note that these are the same units as the sievert. To avoid any risk of confusion between the absorbed dose and the equivalent dose, one must use the corresponding special units, namely the gray instead of the joule per kilogram for absorbed dose and the sievert instead of the joule per kilogram for the dose equivalent. | equivalent dose (of ionising radiation) |
steradian | steradian | sr | solid_angle | 1.0 | steradian | Since the surface area of a sphere is 4*pi*r^2, a sphere measures 4*pi steradians. The steradian is the solid analogue of the radian, and like that unit, is formally dimensionless (in this case, being the ratio of two areas.) | solid_angle |
tesla | Tesla | T | magnetic_flux_density | 1.0 | tesla | The tesla is the value of the total magnetic flux (in some sense, the "power" of a magnet) over area; hence reducing the affected area generally increases the magnetic flux density. Like many of the other electromagnetic units, one tesla is very large. | Magnetic flux density, magnetic inductivity |
v.m-1 | volt per metre | V.m-1 | electric_field_strength | 1.0 | v.m-1 | not yet added | Electric field strength |
volt | Volt | V | electric_potential_difference | 1.0 | volt | The number of volts is a measure of the strength of an electrical source in the sense of how much power is produced for a given current level. It is named in honor of Alessandro Volta (1745–1827), who invented the voltaic pile, the first chemical battery. Since 1990 the volt is maintained internationally for practical measurement using the Josephson effect. | Electrical potential difference, Electromotive force |
w.m-1.k-1 | watt per metre kelvin | W.m-1.K-1 | thermal_conductivity | 1.0 | w.m-1.k-1 | not yet added | Thermal conductivity |
w.m-2 | watt per square metre | W.m-2 | heat_flux_density | 1.0 | w.m-2 | not yet added | heat flux density |
watt | Watt | W | power | 1.0 | watt | The watt dates back to the Second Congress of the British Association of the Advancement of Science in 1889, and is named after James Watt, one of the key engineers to the development of the steam engine. | Power |
weber | Weber | Wb | magnetic_flux | 1.0 | weber | The weber, like the farad, is a very large unit. | Magnetic flux |