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 10^{12} hertz and that has a radiant intensity in that direction of (1/683) watt per steradian. |