The S.I. Base Units

The unit of measurement for any physical quantity is derived from a combination of the seven base units. These base units are:

1. metre (m) -- length
2. kilogram (kg) -- mass
3. second (s) -- time
4. ampere (A) -- amount of electric current
5. kelvin (K) -- temperature
6. candela (cd) -- brightness (of light)
7. mole (mol) -- amount of (chemical) substance

Each of these units is carefully defined and all other measurements are in relation to these definitions (or standards). The page about standards shows how these definitions are made.

A guiding principle of the S.I. units is that new units can be formed from the base units to avoid unneccesarily large or small numbers. This is done through the use of prefixes, which is the subject of the next page.