Abstract

The International System of Units, universally abbreviated SI, and also known as The Modern Metric System, is the dominant system of measurement units used throughout the world, with the exception of the United States.

SI was originally defined in Le Système International d'Unités, a publication by the International Bureau of Weights and Measures (BIPM), located in France. The present article conforms, with certain exceptions for use in the United States, to the latest revision of this document.

A brief history of the evolution of SI is included in the article, as well as a listing of its many advantages. Also included are a description of the seven base units and a number of derived units; a list of the prefixes used with SI and their proper use; a list of some non-SI units used with SI; a list of units used temporarily with SI; and a list of units not to be used.

Some comments concerning units for mass, force, and weight; temperature; pressure and vacuum; energy and torque; nominal dimensions; and dimensionless quantities are also given. A list of rules for style and usage and an explanation of how to handle conversion and rounding are presented.