Guidance for the use of the modern metric system is given. Known as the International System of Units (abbreviated SI), the system is the basis for worldwide standardization of measurement units. Information is included on SI, a list of units recognized for use with SI, and a list of conversion factors, together with general guidance on proper style and usage.

This document is the primary American National Standard on application of the metric system. It emphasizes use of the International System of Units (SI), which is the modern, internationally accepted metric system. It includes information on SI, a limited list of units recognized for use with SI, and a list of conversion factors, together with general guidance on style and usage. It also lists older “metric” units that shall no longer be used. The word primary implies that other metric standards in the United States should be consistent with this document.

The purpose of the standard is to give guidance on metric practice and the use of SI.