Quantities and units

ISO has published the International Standards ISO 31, Quantities and units (14 parts) and ISO 1000, SI units and recommendations for the use of their multiple and of certain other units for the application of the SI.

SI denotes Système International d'Unités, i.e. the International System of Units. The letters SI are used in all languages to denote this system.

The SI is a system of units adopted by the highest international authority on units, i.e. the General Conference on Weights and Measures (Conférence Général des Poids et Mesures, CGPM). It is founded on older metric systems, and has been designed to be suitable for use in every context - customary, technical, and scientific.

The SI is built in such a way that only one unit is used for each kind of quantity. This makes the total number of units less and the system becomes easier to learn and to use.

The structure of the system also makes calculations easier. The benefits of the SI are most evident when its rules are applied consistently.

ISO has also published the ISO standards handbook Quantities and units, containing the complete set of the ISO 31 standards, as well as ISO 1000.