This standard describes the International System of Units (SI), the modern version of the metric system. It includes listings of the base units, supplementary units, and units derived therefrom. Guidance is provided on application of the SI prefixes, other units in use with SI (including units accepted for limited use and units to be abandoned), and unit selection. A section on style and usage covers the writing of unit symbols and names, pronunciation, and recommendations for numbers. Extensive guidance is provided on conversion and rounding including tables for conversion of linear dimensions, also pressure and stress, along with a very extensive table of conversion factors. An appendix provides background information in the development of SI.

This standard gives guidance for application of the modernized metric system in the United States. The International System of Units, developed and maintained by the General Conference on Weights and Measures (abbreviated CGPM from the official French name Conference Generate des Poids et Mesures) is intended as a basis for worldwide standardization of measurement units. The name International System of Units and the international abbreviation SI2 were adopted by the 11th CGPM in 1960. SI is a complete, coherent system that is being universally adopted. 1.2 Information is included on SI, a limited list of non-SI units recognized for use with SI units, and a list of conversion factors from non-SI t o SI units, together with general guidance on proper style and usage. 1.3 It is hoped that an understanding of the system and its characteristics, and careful use according to this standard, will help to avoid the degradation that has occurred in all older measurement systems.