The SI system of units defines seven SI base units: physical units defined by an operational definition.

All other physical units can be derived from these base units: these are known as SI derived units. Derivation is by dimensional analysis. Use SI prefixes to abbreviate long numbers.

The following are the base units from which all others are derived. They are dimensionally independent, with the exception of the candela. The candela was formerly a fundamental unit but has been redefined in terms of the other SI base units. Despite this, it is still considered a base unit for historical reasons.

See also

• SI
• SI derived unit
• SI prefix

External links

• BIPM
• NPL - Kilogram
• NIST -SI

SI units | Dimensional analysis

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