Derived units with special names in the SI |
Derived quantity | SI coherent derived unit ^{(a)} |
Name | Symbol | Expressed in terms of SI base units |
1 | plane angle | radian ^{(b)} | rad | m/m = 1 |
2 | solid angle | steradian ^{(b)} | sr ^{(c)} | m^{2}/m^{2}=1 |
3 | frequency | hertz ^{(a)} | Hz | s^{-1} |
4 | force | newton | N | m kg s^{-2} |
5 | pressure, stress | pascal | Pa | N/m^{2} = m^{-1} kg s^{-2} |
6 | energy, work, amount of heat | joule | J | N m = m^{2} kg s^{-2} |
7 | power, radiant flux | watt | W | J/s = m^{2} kg s^{-3} |
8 | electric charge, amount of electricity | coulomb | C | s A |
9 | electric potential difference, electromotive force | volt | V | W/A = m^{2} kg s^{-3} A^{-1} |
10 | capacitance | farad | F | C/V = m^{-2} kg^{-1} s^{4} A^{2} |
11 | electric resistance | ohm | Ω | V/A = m^{2} kg s^{-3} A^{-2} |
12 | electric conductance | siemens | S | A/V = m^{-2} kg^{-1} s^{3} A^{2} |
13 | magnetic flux | weber | Wb | V s = m^{2} kg s^{-2} A^{-1} |
14 | magnetic flux density | tesla | T | Wb/m^{2} = kg s^{-2} A^{-1} |
15 | inductance | henry | H | Wb/A = m^{2} kg s^{-2} A^{-2} |
16 | Celsius temperature | degree Celsius ^{(e)} | °C | K |
17 | luminous flux | lumen | lm | cd sr ^{(c)} = cd |
18 | illuminance | lux | lx | lm/m^{2} = m^{-2} cd |
19 | activity referred to a radionuclide ^{(f)} | becquerel ^{(d)} | Bq | s^{–1} |
20 | absorbed dose, specific energy (imparted), kerma | gray | Gy | J/kg = m^{2} s^{-2} |
21 | dose equivalent, ambient dose equivalent, directional dose equivalent, personal dose equivalent | sievert (g) | Sv | J/kg = m^{2} s^{-2} |
22 | 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) The name gray should be used instead of joules per kilogram for the unit of absorbed dose D of ionizing radiation, and the name sievert instead of joules per kilogram for the unit of dose equivalent H, which is the product of the absorbed dose D and the dimensionless quality factor Q. |