National Physical Laboratory

Why are there seven base units in the SI system? (FAQ - Quantum)

The international system is a set of seven base units chosen to fulfil the requirements of science and technology. The selection of seven base units is a matter of choice. This choice is the responsibility of the International Committee of Weights and Measures (CIPM) which has representatives from many countries and with the help of its advisory committees is responsible for defining and maintaining the SI . The base units are to a certain extent an arbitrary choice and when the metric system was set up a three dimensional mechanical system was chosen with the meter kilogram and second as base units. This was later extended to a four dimensional system to include the ampere. Subsequently the kelvin, candela and then the mole were added bringing the number to seven.

Last Updated: 20 Mar 2012
Created: 9 Aug 2007


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