SI is abbreviation for Système International d’Unités (in French), in English it means International system of Units. It is the modern form of metric units and it is the most widely used system of measurement, accepted by most countries. It contains seven base units.
metre | length | ||
kilogram | mass | ||
second | time | ||
ampere | electric current | ||
kelvin | thermodynamic temperature | ||
mole | amount of substance | ||
candela | luminous intensity |
Other quantities, called derived quantities, are defined in terms of the seven base units over different equations, like area (m×m=m^{2}), speed (m/s) etc. Some derived units got special name, like Newton (N=kg×m/s^{2}), Pascal (Pa = N/m^{2}), etc.
Derived quantity | Name | Symbol | Expression in terms of other SI units | Expression in terms of SI base units |
---|---|---|---|---|
plane angle | radian | rad | - | m·m^{-1 }= 1 |
solid angle | steradian | sr | - | m^{2}·m^{-2 }= 1 |
frequency | hertz | Hz | - | s^{-1} |
force | newton | N | - | m·kg·s^{-2} |
pressure, stress | pascal | Pa | N/m^{2} | m^{-1}·kg·s^{-2} |
energy, work, quantity of heat | joule | J | N·m | m^{2}·kg·s^{-2} |
power, radiant flux | watt | W | J/s | m^{2}·kg·s^{-3} |
electric charge, quantity of electricity | coulomb | C | - | s·A |
electric potential difference, electromotive force |
volt | V | W/A | m^{2}·kg·s^{-3}·A^{-1} |
capacitance | farad | F | C/V | m^{-2}·kg^{-1}·s^{4}·A^{2} |
electric resistance | ohm | V/A | m^{2}·kg·s^{-3}·A^{-2} | |
electric conductance | siemens | S | A/V | m^{-2}·kg^{-1}·s^{3}·A^{2} |
magnetic flux | weber | Wb | V·s | m^{2}·kg·s^{-2}·A^{-1} |
magnetic flux density | tesla | T | Wb/m^{2} | kg·s^{-2}·A^{-1} |
inductance | henry | H | Wb/A | m^{2}·kg·s^{-2}·A^{-2} |
Celsius temperature | degree Celsius | °C | - | K |
luminous flux | lumen | lm | cd·sr | m^{2}·m^{-2}·cd = cd |
illuminance | lux | lx | lm/m^{2} | m^{2}·m^{-4}·cd = m^{-2}·cd |
activity (of a radionuclide) | becquerel | Bq | - | s^{-1} |
absorbed dose, specific energy (imparted), kerma | gray | Gy | J/kg | m^{2}·s^{-2} |
dose equivalent | sievert | Sv | J/kg | m^{2}·s^{-2} |
catalytic activity | katal | kat | s^{-1}·mol |
Source: NIST.gov, SI base- and derived units physics.nist.gov/cuu/Units/units.html