The International System of Units (SI) defines seven units as a basic set from which all other SI units are derived. These SI base units and their physical quantities are:
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metre for length
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kilogram for mass
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second for time
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ampere for electric current
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kelvin for temperature
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candela for luminous intensity
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mole for the amount of substance.
The SI base quantities form a set of mutually independent dimensions as required by dimensional analysis.
Metre, m | length |
|
Kilogran, kg | mass | Equal to the mass of the international prototype of the kilogram |
Second, s | time | Duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of caesium 133. |
ampere, A | electric current | The current through each of two straight parallel conductors of infinite length, negligible cross-section, 1 metre apart in a vacuum, which would a force equal to |
Kelvin, K | Absolute temperature | Equal to the fraction 1/273.16 of the thermodynamic temperature of the triple point of water |
Mole, mol | amount of substance | The amount of substance which contains as many elementary entities - atoms, molecules, ions, electrons, other particles, or specified groups of such particles - as atoms in 12g carbon 12 |
Candela, cd | luminosity | The luminous intensity of a source that emits monochromatic radiation of frequency |
of the distance travelled by light in one second.
newton per metre of length
hertz and that has a radiant intensity in that direction of 1/683 watt per steradia (solid angle).