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SI derived unit

SI derived units are part of the SI system of measurement units and are derived from the seven SI base units.


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


  • 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)

Last updated: 10-18-2005 13:21:44
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