Base units
There are 76mutally independent base units, from which all other physical units are derived. They are based on the definitions of some universal constants of nature, such as, among others, the speed of light in vacuum, the constants of Avogadro, Boltzmann and Planck, and the electron charge.
| unit | symbol | quantity | definition |
|---|---|---|---|
| second | s | time | ground-state hyperfine transition frequency νhf of 133Cs = 9,192,631,770 Hz *) |
| meter | m | length | speed of light c in vacuum = 299,792,458 m/s |
| kilogram | kg | mass | Planck's constant h = 6.626,070,15·10-34 J·s **) |
| ampere | A | current | electron charge e = 1.602,176,634·10-19 A·s |
| kelvin | K | temperature | Boltzmann's constant kB = 1.380,649·10-23 J/K **) |
| mole | mol | matter | Avogadro's constant NA = 6.022,140,76·1023 particles per mole |
| candela | cd | luminous intensity | 1 candela = luminous intensity of standard source ***) |
*) 1 Hz = 1 s-1
**)
1 J = 1 kg·m2·s-2
***) radiation source with a frequency of 540·1012 Hz and emitting een energy of 1/683 J per second and per steradian
Related concepts
Last modified:21 December 2025 9.38 p.m.
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