power-of-ten) multiples and sub-multiples of the coherent unit. Since the sizes of coherent units will be convenient for only some applications and not for others, the SI provides twenty prefixes which, when added to the name and symbol of a coherent unit produce twenty additional (non-coherent) SI units for the same quantity these non-coherent units are always decimal (i.e. The seven base units and the 22 coherent derived units with special names and symbols may be used in combination to express other coherent derived units. Twenty-two coherent derived units have been provided with special names and symbols.

These are called coherent derived units, which can always be represented as products of powers of the base units. The system can accommodate coherent units for an unlimited number of additional quantities. The SI comprises a coherent system of units of measurement starting with seven base units, which are the second (symbol s, the unit of time), metre (m, length), kilogram (kg, mass), ampere (A, electric current), kelvin (K, thermodynamic temperature), mole (mol, amount of substance), and candela (cd, luminous intensity). : 123 Established and maintained by the General Conference on Weights and Measures (CGPM ), it is the only system of measurement with an official status in nearly every country in the world, employed in science, technology, industry, and everyday commerce. The International System of Units, known by the international abbreviation SI in all languages : 125 : iii and sometimes pleonastically as the SI system, is the modern form : 117 of the metric system and the world's most widely used system of measurement.

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