Note that the symbols used for each unit are symbols, not abbreviations, and should not be capitalized or followed by a period. i.e. metre = m, not m., or M., and kilogram = kg, not K.g., KG., or KGr.
| Unit | Physical Quantity | Symbol | Definition |
|---|---|---|---|
| metre | length | m | The length of path travelled by light in a vacuum during the time interval of 1/299 792 458 of a second (17th CPGM, 1983); originally 1/10 000 000 of the distance from the North Pole to the Equator through Paris, France. |
| kilogram | mass | kg | The mass equal to the International Prototype of the kilogram (3rd CPGM, 1901) originally defined as the mass of 1 dm3 (1 litre) of water at 4°C. |
| second | time | s | The duration of 9 192 631 770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom (13th CGPM, 1967). |
| ampere | electric current | A | The constant of current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in a vacuum, would produce between these conductors a force equal to 2 x 10-7 newton per metre of length (9th CGPM, 1948). |
| kelvin | thermodynamic temperature | K | The fraction 1/273.16 of the thermodynamic triple point of water (13th CGPM, 1967) (approximately the fraction 1/100 of temperature difference between the freezing point and boiling point of water at 101.315 kPa pressure). |
| mole | amount of a substance | mol | The amount of a substance of a system which contains as many elementary entities (atoms, molecules, ions, electrons, or other particles or specified groups of particles) as there are atoms in 0.012 kilogram of carbon-12. (14th CGPM, 1971). |
| candela | luminous intensity | cd | 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 (16th CGPM, 1979). |
