SI base units
All physical values can be described algebrically in terms of 7 basic and independed units, called the SI base units.
Base unit category Unit name Unit symbole Definition
Length meter m The meter is equal to the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.
Mass kilogram kg The kilogram is equal to the mass of the international prototype of the kilogram and kept in Paris.
Time second s The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.
Electric current ampere A The ampere is the current which, if applied in two straight parallel conductors of infinite length and 1 meter apart in vacuum, whould produce a force of
2.0 X 10-7 newton per meter of length.
Thermodynamic temperature Kelvin K The Kelvin scale of temperature has its origin (0 value) at absolute temperature and has a fixed point at the triple point of water defined as 273.16 Kelvin.
Amount of substance Mole mol The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12.
Luminous intensity Candela cd The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 X 1012 hertz and that has a radiant intensity in that direction of (1/683) watt per steradian.