SI derived unit
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SI derived units are part of the SI system of measurement units and are derived from the seven SI base units.
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Units with special names and symbols
| Physical quantity | Name of SI unit | Symbol for SI unit | Expression in terms of other units | Expression in terms of SI base units | |
|---|---|---|---|---|---|
| plane angle | radian | rad | 1 | m · m-1 | |
| solid angle | steradian | sr | 1 | m2 · m-2 | |
| frequency | hertz | Hz | s-1 | ||
| force, weight | newton | N | kg · m · s-2 | ||
| pressure, stress | pascal | Pa | N · m-2 | kg · m-1 · s-2 | |
| energy, work, heat | joule | J | N · m | kg · m2 · s-2 | |
| power, radiant flux | watt | W | J · s-1 | kg · m2 · s-3 | |
| electric charge | coulomb | C | A · s | ||
| electric potential, electromotive force | volt | V | J · C-1 | kg · m2 · s-3 · A-1 | |
| electric capacitance | farad | F | C · V-1 | kg-1 · m-2 · s4 · A2 | |
| electrical resistance, impedance, reactance | ohm | Ω | V · A-1 | kg · m2 · s-3 · A-2 | |
| electric conductance | siemens | S | A · V-1 | kg-1 · m-2 · s3 · A2 | |
| magnetic flux | weber | Wb | V · s | kg · m2 · s-2 · A-1 | |
| magnetic flux density, magnetic inductivity | tesla | T | V · s · m-2 | kg · s-2 · A-1 | |
| inductance | henry | H | V · s · A-1 | kg · m2 · s-2 · A-2 | |
| temperature | degree Celsius | °C | K - 273.15 | ||
| luminous flux | lumen | lm | cd · sr | cd | |
| illuminance | lux | lx | cd · sr · m-2 | cd · m-2 | |
| activity (radioactive) | becquerel | Bq | s-1 | ||
| absorbed dose (of radiation) | gray | Gy | J · kg-1 | m2 · s-2 | |
| dose equivalent (dose equivalent index) | sievert | Sv | Gy | m2 · s-2 | |
| catalytic activity | katal | kat | mol · s-1 | ||
Other quantities and units
| Physical quantity | Name of SI unit | Symbol for SI unit | Expression in terms of SI base units |
|---|---|---|---|
| area | square metre | m2 | |
| volume | cubic metre | m3 | |
| speed, velocity | metre per second | m · s-1 | |
| acceleration | metre per second squared | m · s-2 | |
| angular velocity | radian per second | rad · s-1 | s-1 |
| momentum | newton second | N · s | kg · m · s-1 |
| angular momentum | newton metre second | N · m · s | kg · m2 · s-1 |
| moment of force | newton metre | N · m | kg · m2 · s-2 |
| wavenumber | reciprocal metre | m-1 | |
| density, mass density | kilogram per cubic metre | kg · m-3 | |
| specific volume | cubic metre per kilogram | kg-1 · m3 | |
| amount (-of-substance) concentration | mole per cubic metre | m-3 · mol | |
| molar volume | cubic metre per mole | m3 · mol-1 | |
| heat capacity, entropy | joule per kelvin | J · K-1 | kg · m2 · s-2 · K-1 |
| molar heat capacity, molar entropy | joule per kelvin mole | J · K-1 · mol-1 | kg · m2 · s-2 · K-1 · mol-1 |
| specific heat capacity, specific entropy | joule per kilogram kelvin | J · K-1 · kg-1 | m2 · s-2 · K-1 |
| molar energy | joule per mole | J · mol-1 | kg · m2 · s-2 · mol-1 |
| specific energy | joule per kilogram | J · kg-1 | m2 · s-2 |
| energy density | joule per cubic metre | J · m-3 | kg · m-1 · s-2 |
| surface tension | newton per metre | N · m-1 = J · m-2 | kg · s-2 |
| heat flux density, irradiance | watt per square metre | W · m-2 | kg · s-3 |
| thermal conductivity | watt per metre kelvin | W · m-1 · K-1 | kg · m · s-3 · K-1 |
| kinematic viscosity, diffusion coefficient | square metre per second | m2 · s-1 | |
| dynamic viscosity | pascal second | Pa · s = N · s · m-2 | kg · m-1 · s-1 |
| electric charge density | coulomb per cubic metre | C · m-3 | m-3 · s · A |
| electric current density | ampere per square metre | A · m-2 | |
| conductivity | siemens per metre | S · m-1 | kg-1 · m-3 · s3 · A2 |
| molar conductivity | siemens square metre per mole | S · m2 · mol-1 | kg-1 · s3 · mol-1 · A2 |
| permittivity | farad per metre | F · m-1 | kg-1 · m-3 · s4 · A2 |
| permeability | henry per metre | H · m-1 | kg · m · s-2 · A-2 |
| electric field strength | volt per metre | V · m-1 | kg · m · s-3 · A-1 |
| magnetic field strength | ampere per metre | A · m-1 | |
| luminance | candela per square metre | cd · m-2 | |
| exposure (X and gamma rays) | coulomb per kilogram | C · kg-1 | kg-1 · s · A |
| absorbed dose rate | gray per second | Gy · s-1 | m2 · s-3 |
Conversion between kelvins and degrees Celsius
One degree Celsius is equal to 1 kelvin.
Temperature in degrees Celsius = Temperature in kelvins - 273.15. Thus, one could think of the Kelvin scale as the same as the Celsius scale, with its zero point moved down to absolute zero. That is historically accurate; however, it has become more convenient to fix the standard for the kelvin, and thus the Celsius scale is derived from that standard (i.e., it now depends on absolute zero and the triple point of water with a 0.01 K offset—the boiling point of water no longer has anything to do with the official definition of degrees Celsius).
Temperature differences are often measured in degrees Celsius; however, it doesn't matter: differences in temperature are equivalent whether kelvins or degrees Celsius are used.
See also
References
- I. Mills, Tomislav Cvitas, Klaus Homann, Nikola Kallay, IUPAC: Quantities, Units and Symbols in Physical Chemistry, 2nd edition (June 1993), Blackwell Science Inc (p. 72)
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