As of August 16, 2023 the physics.nist.gov historic SI Units site has permanently retired. This page and complete Metric (SI) Program contains current SI information. Contact TheSI [at] nist.gov with comments, questions or concerns.
Federal Register Notice
FR 28432-28433 (PDF)
Edition: May 16, 2008
Together NIST SP 330 and NIST SP 811 provide the legal interpretation of and guidelines for the use of the SI in the United States, as described in the Interpretation of the International System of Units (the Metric System of Measurement) for the United States.
The International System of Units (SI)
NIST SP 330
This 2019 edition of NIST Special Publication (SP) 330 is the United States version of the English text of the ninth edition of the Bureau International des Poids et Mesures (BIPM) SI Brochure (the most current) published in 2019. The 2019 edition of NIST SP 330 replaces its immediate predecessor, the 2008 edition.
Guide for the Use of International System of Units (SI)
NIST SP 811
This document gives the rules and style conventions for printing and using units, unit symbols and SI prefix symbols. The publication includes an editorial checklist for reviewing manuscripts' conformity with the SI and the basic principles of physical quantities and units. Appendix A provides the definitions of the SI base units. Appendix B gives conversion factors for converting values of quantities expressed in units that are mainly unacceptable to use with the SI to values expressed mainly in units of the SI. Appendix B also includes a simplified discussion of rounding numbers and rounding converted numerical values of quantities. This 2008 edition supersedes NIST Special Publication 811, 1995 Edition, April 1995.
NIST SP 1247 SI Base Units Relationships Poster (PDF)
This publication is a colorful poster illustrating the relationships of the International System of Units (SI) derived units with special names and symbols and the seven traditional base units.
The International System of Units (SI) - Conversion Factors for General Use
NIST SP 1038 (PDF)
This publication lists the units of the International System of Units (SI), or metric system, recommended for use in trade and commerce and other general uses by the National Institute of Standards and Technology. Much of the information in SP 1038 was based on the historic standard Fed-Std-376B: 1993, Preferred Metric Units for General Use by the Federal Government.
NIST SI Measurement System Chart
This publication is a colorful chart explaining the 7 base units of the SI (International System of Units) and prefix symbols, featuring the Measurement League: Guardians of the SI. The Measurement League are superheroes dedicated to the fight against uncertainty, imprecision, and inaccuracy and to improving the quality of our lives and the things we build. SI Prefix symbols are featured in the chart and used to represent smaller or larger units by factors that are powers of 10. Submit hard copy requests to TheSI [at] nist.gov. Chart dimensions: 216 mm by 279 mm (8.5 in by 11 in).
Metric Style Guide
NIST LC 1137 (PDF)
The "Metric Style Guide" addresses how to use metric units in written and verbal communication by addressing the metric prefixes, proper spelling of terms, how to make conversions, use of symbols, plurals, pronunciation, and decimal points. (Out of Print).
U.S. Manufactures with Product Conforming to Metric Standards: An Analysis (PDF)
This report, prepared for the Metric Program, is the result of research into and analysis of the unique data on U.S. manufacturers maintained by the Thomas Publishing Company.
The purpose of this research and analysis is to provide the Metric Program with insights as to the current extent of compliance to metric standards among U.S. industrial product manufacturers. This report gives a "snapshot" of the degree of availability of metric standard products of interest to original equipment manufacturers serving both domestic and overseas markets. (Out of Print).
Report to the Congress. A Metric America: A decision whose time has come.
NBS SP 345 (PDF)
Edition: July 1971
In 1968, Congress authorized the Secretary of Commerce to make a study to determine the advantages and disadvantages of increased use of the metric system in the United States (Public Law 90-472). This report and 12-volume substudy report series contributed to passage of the Metric Conversion Act of 1975 (15 U.S.C. 205a et seq., amended by the Omnibus Trade and Competitiveness Act of 1988). (Out of Print).
The International Bureau of Weights and Measures (1875 to 1975)
NBS SP 420 (PDF)
Edition: July 1975
This publication provides a history of the first century (1875-1975) of the International Bureau of Weights and Measures (BIPM, Bureau International des Poids et Mesures), including the history of the Meter Convention (Convention du Mètre) and the SI. (Out of Print).
NEST-R (STEM Registry)