system of units, based on the International System of Quantities, their names and symbols, including a series of prefixes and their names and symbols, together with rules for their use, adopted by the General Conference on Weights and Measures (CGPM)
NOTE 1 The SI is founded on the seven base quantities of the ISQ and the names and symbols of the corresponding base units that are contained in the following table.
Base quantity | Base unit | |
Name | Name | Symbol |
length | metre | m |
mass | kilogram | kg |
time | second | s |
electric current | ampere | A |
thermodynamic temperature | kelvin | K |
amount of substance | mole | mol |
luminous intensity | candela | cd |
NOTE 2 The base units and the coherent derived units of the SI form a coherent set, designated the “set of coherent SI units”.
NOTE 3 For a full description and explanation of the International System of Units, see the current edition of the SI brochure published by the Bureau International des Poids et Mesures (BIPM) and available on the BIPM website.
NOTE 4 In quantity calculus, the quantity 'number of entities' is often considered to be a base quantity, with the base unit one, symbol 1.
NOTE 5 The SI prefixes for multiples of units and submultiples of units are:
Factor | Prefix | |
Name | Symbol | |
1024 | yotta | Y |
1021 | zetta | Z |
1018 | exa | E |
1015 | peta | P |
1012 | tera | T |
109 | giga | G |
106 | mega | M |
103 | kilo | k |
102 | hecto | h |
101 | deca | da |
10-1 | deci | d |
10-2 | centi | c |
10-3 | milli | m |
10-6 | micro | µ |
10-9 | nano | n |
10-12 | pico | p |
10-15 | femto | f |
10-18 | atto | a |
10-21 | zepto | z |
10-24 | yocto | y |