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Units with special names and symbols; units that incorporate special names and symbols
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Summary
Derived units expressed in terms of base units
Units with special names and symbols; units that incorporate special names and symbols
Units for dimensionless quantities, also called quantities of dimension one

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SI brochure, Table 3 (Section 2.2.2)


Table 3. Coherent derived units in the SI with special names and symbols

Derived quantity SI coherent derived unit (a)
Name Symbol Expressed
in terms of
other SI units
Expressed
in terms of
SI base units
plane angle radian (b) rad 1 (b) m/m
solid angle steradian (b) sr (c) 1 (b) m2/m2
frequency hertz (d) Hz   s–1
force newton N   m kg s–2
pressure, stress pascal Pa N/m2 m–1 kg s–2
energy, work, amount of heat joule J N m m2 kg s–2
power, radiant flux watt W J/s m2 kg s–3
electric charge, amount of electricity coulomb C   s A
electric potential difference, electromotive force volt V W/A m2 kg s–3 A–1
capacitance farad F C/V m–2 kg–1 s4 A2
electric resistance ohm capital omega V/A m2 kg s–3 A–2
electric conductance siemens S A/V m–2 kg–1 s3 A2
magnetic flux weber Wb V s m2 kg s–2 A–1
magnetic flux density tesla T Wb/m2 kg s–2 A–1
inductance henry H Wb/A m2 kg s–2 A–2
Celsius temperature degree Celsius (e) °C   K
luminous flux lumen lm cd sr (c) cd
illuminance lux lx lm/m2 m–2 cd
activity referred to a radionuclide (f) becquerel (d) Bq   s–1
absorbed dose, specific energy (imparted), kerma gray Gy J/kg m2 s–2
dose equivalent,
ambient dose equivalent,
directional dose equivalent,
personal dose equivalent
sievert (g) Sv J/kg m2 s–2
catalytic activity katal kat   s–1 mol

(a) The SI prefixes may be used with any of the special names and symbols, but when this is done the resulting unit will no longer be coherent.
(b) The radian and steradian are special names for the number one that may be used to convey information about the quantity concerned. In practice the symbols rad and sr are used where appropriate, but the symbol for the derived unit one is generally omitted in specifying the values of dimensionless quantities.
(c) In photometry the name steradian and the symbol sr are usually retained in expressions for units.
(d) The hertz is used only for periodic phenomena, and the becquerel is used only for stochastic processes in activity referred to a radionuclide.
(e) The degree Celsius is the special name for the kelvin used to express Celsius temperatures. The degree Celsius and the kelvin are equal in size, so that the numerical value of a temperature difference or temperature interval is the same when expressed in either degrees Celsius or in kelvins.
(f) Activity referred to a radionuclide is sometimes incorrectly called radioactivity.
(g) See CIPM Recommendation 2 (CI-2002) on the use of the sievert.
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Note: For the official text, please refer to the PDF files available at:
  • http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf (in English) and
  • http://www.bipm.org/utils/common/pdf/si_brochure_8_fr.pdf (in French).
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