Here are basic data associated with the International System of Units, commonly known as the "metric system". The abbreviation "SI" is from the French expression Système Internationale [d'Unités].
Several people come here really seeking a Metric Conversion Chart.
|SI base units|
|length||metre||m||length of the path travelled by light in vacuum during a time interval of 1/299 792 458 second.|
|mass||kilogram||kg||mass of international prototype.|
|time||second||s||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 cæsium-133 atom.|
|electric current||ampere||A||the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 metre apart in vacuum would produce between these conductors a force equal to 2 × 10-7 newton per square metre of length.|
|thermodynamic temperature||kelvin||K||the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.|
|amount of substance||mole||mol||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 luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.|
|SI derived units|
|plane angle||radian||rad||the plane angle between two radii of a circle that cut off on the circumference an arc equal in length to the radius|
|solid angle||steradian||sr||solid angle that, having its vertex in the centre of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere.|
|frequency||hertz||Hz||1 / s|
|force||newton||N||m kg / s²|
|pressure||pascal||Pa||N / m²|
|power||watt||W||J / s|
|electric charge||coulomb||C||A s|
|electric potential||volt||V||W / A|
|capacitance||farad||F||C / V|
|resistance||ohm||Ω||V / A|
|conductance||siemens||S||A / V|
|magnetic flux||weber||Wb||V s|
|magnetic flux density||tesla||T||Wb / m²|
|inductance||henry||H||Wb / A|
|luminous flux||lumen||lm||cd sr|
|illuminance||lux||lx||lm / m²|
|Units which may or may not be a part of the International System of Units (I just don't know)|
|radiation dose||sievert||Sv||J / kg|
|enzyme activity||katal||kat||mol / s|
|Prefixes used with SI units|
Prefixes are usually added onto the names of the base or derived units. The resultant word is best accented on the first syllable. For example, 1000 metres is 1 kilometre (1000 m = 1 km), pronounced KILL-a-me-ter / ˈkɪləˌmitɚ /.
But, with the kilogram, we pretend as though the base unit be the "gram" (1/1000 kg) for purposes of forming quantities of variant magnitudes: e.g., one millionth of a kilogram is not a microkilogram (µkg) but a milligram (mg).