SI Base Units
The SI (Système International d'Unités) is a globally agreed system of units, with seven base units.
Formally agreed by the 11th General Conference on Weights and Measures (CGPM) in 1960, the SI is at the centre of all modern science and technology. The definition and realisation of the base and derived units is an active research topic for metrologists with more precise methods being introduced as they become available.
Download NPL's 'Units of measurement' poster