The name

*Système International d'Unités* (International System of Units) was adopted in 1960. The abbreviation and/or symbol for this is

SI (no full stops). This renamed the

MKSA, the then-current scientific form of the

metric system.

__The history of the SI in brief:__

**1799** Platinum standard *mètre* and *kilogramme* deposited in Paris. Metric system official in France and soon spreads to most European countries.

**1832** Gauss uses a system of measurement using the second (defined by astronomy) and the two metric units the millimetre and the gram as its basis. He and Weber then extend its use to electrical measurements.

**1874** The British Association for the Advancement of Science (BAAS), under the guidance of Maxwell and Kelvin, adopts the CGS system, a coherent system of units with the centimetre, gram, and second as their basis, and derived units in terms of these. They adopt the prefixes mega and micro to supplement the original French prefixes (from milli to myria = 10000).

**1875** The Treaty of the Metre signed in Sèvres, in France, establishes the world body that controls the metric system, the BIPM (*Bureau Internationale des Poids et Mesures*).

**1889** The BIPM adopts the MKS, a coherent system of units using a new platinum prototype metre and kilogram together with the astronomical second as its basis.

**1939** MKSA system proposed, which brings electrical and magnetic units into conformity with the MKS by rewriting equations so that the ampere can be used as a fourth base unit.

**1954** The BIPM officially extends the MKS system to include three new base units, the ampere, the kelvin, and the candela.

**1960** The name Système International d'Unités, symbolized SI, was adopted.

**1971** A seventh base unit, the mole, was introduced to the SI.

This node with its long title can serve as a history. For details of all the SI units now used, see SI units.

For details of the prefixes for multiples and submultiples, see Standard SI prefixes.

For a history of the metric system generally, and uses and conversions of all the everyday (non-scientific) units such as the litre, centimetre, degree Celsius, and nautical mile, see metric system.