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Metric (SI) Program

The Metric Program helps implement the national policy to establish the SI (International System of Units, commonly known as the metric system) as the preferred system of weights and measures for U.S. trade and commerce. It provides leadership and assistance on SI use and conversion to federal agencies, state and local governments, businesses, trade association, standards development organizations, educators, and the general public.

Collage of photos, baby with thermometer, orange juice in bottles, hand holding a pen against a board and measuring tape, boat with crates on it

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 (TheSI[at]nist[dot]gov) with comments, questions or concerns.

The Metric Program is focused on increasing the International System of Units (SI) use in:

Trade and Commerce

Because of the importance of the International System of Units (SI), commonly known as the metric system) as an international standard, its use in product design, manufacturing, marketing, and labeling is essential for U.S. industry's success in the global marketplace. The NIST Metric Program encourages the use of the SI in all facets of education, including honing of worker skills. Resources include:

  • SI Basics - Explore elements of the SI, including the defining constants, base units, prefixes, and useful definitions.
  • Professional development training and occupational resources will help expand SI subject-matter knowledge and skills. Opportunities are available through out the year. Ideal for pre-service teachers, in-service teachers, and other professionals.
  • U.S. Metrication resources support the voluntary shift from the us of customary measurement units to the SI.
  • Juice cartons showing different labeling formats
    Credit: NIST Juice cartons showing different labeling formats
    PROJECT: Expand Labeling Options to Benefit U.S. Exports - A Proposal to Amend the Federal Fair Packaging and Labeling Act (FPLA). To facilitate the expansion of U.S. manufacturer exports, NIST recommends updating the FPLA to create a new package labeling option to provide U.S. manufacturers increased flexibility when labeling packaged products. The FPLA requires packaged goods to bear essential information that informs consumers about the product, including how much commodity is contained within the package. U.S. manufacturers are limited to a "dual unit" format, prohibited by Federal law from declaring the net quantity using only the "metric" option, while foreign competitors have the advantage of using a simpler format. This proposal has been developed in response to U.S. manufacturer and consumer requests.

All Levels of Government

The Metric Program coordinates metric transition activities under the Metric Conversion Act, including transition of all federal agencies (Executive Order 12770). U.S. metric legislation and policy authorizes Secretary of Commerce to direct and coordinate the federal agency metric transition and to assess progress. Federal agencies implement formal policy and plans for using the SI (metric system) and report transition progress. The use of the SI in federal agency programs relating to trade, industry, and commerce is intended to support industry's voluntary adoption of the SI.

  • U.S. Survey Foot is obsolete
    The U.S. survey foot is obsolete.
    Credit: NIST
    PROJECT: U.S. Survey Foot Retirement. On January 1, 2023 the U.S. survey foot was deemed obsolete and the international foot definition officially superseded the U.S. survey foot. This retirement was planned by the National Oceanic and Atmospheric Administration (NOAA) and NIST for several years to provide national uniformity in the measurement of length and to move towards more precise positioning in surveying, mapping, and engineering. NOAA National Geodetic Survey (NGS) has long used the meter as its official unit of measurement and this will not change. Currently, the international foot is based on the meter and all U.S. customary units are based on the International System of Units (SI).

Everyday Life within the United States

Progress toward greater use of the SI (metric system) continues in the United States. Many are not aware that "below the surface" the SI is the foundation for all measurements or of the extent the SI is used by industry to manufacture and supply the goods and services consumers use every day. While it's true that metric use is is mandatory in some countries and voluntary in others, all countries have recognized and adopted the SI, including the United States. Busting Myths about the Metric System explores several common misconceptions about U.S. metrication.

  • guide to the SI covers
    Guides to the SI
    Technical guides and information are available to assist in the use and application of the SI in a broad spectrum of technical activities.
    The BIPM SI Brochure, NIST Special Publication (SP) 330, NIST Special Publication (SP) 811 are available to help with proper SI usage, the basic principles concerning quantities and units, writing with SI units, and help review the conformity of manuscript and other documents.
    Explore additional information on SI Units, including the seven (7) defining constants, seven (7) base units, and more!
  • Learn more about every day use of metric measurements.
  • Become familiar with the SI, which is easy to learn and use. Develop a few reference points to build an innate understanding of "how much."
  • Everyday estimation is more than taking a guess! The ability to interpret measurement scale and approximate at quantity helps interpret the world around us.
  • NIST metric kitchen
    Credit: NIST
    PROJECT: NIST Metric Kitchen. Select and enjoy preparing a NIST metric recipe! Cooking and baking are ideal for becoming familiar with the metric system, teaching Science, Technology, Engineering, and Math (STEM), as well as measurement sense making. A recipe gallery, culinary measurement tips, cookware and tools, and temperature guidance has been developed to assist in building experience using a kitchen scale to measure ingredients in grams and K-12 educators that teach cooking techniques and related life skills topics in the classroom.
  • PROJECT: National Metric Week. Communities across the country observe Metric Week, an educational holiday that raises awareness about the metric system and the benefits of use in every day life. Accept this invitation to celebrate the 7 SI base units with 7 days of measurement fun during the week containing the tenth day of the tenth month (10/10).

Resources

Events

5854 Mass Metrology Seminar

Mon, Feb 26 - Fri, Mar 8 2024
The Mass Metrology Seminar is a two-week, "hands-on" seminar. It incorporates approximately 30 percent lectures and 70

5905 Volume Metrology Seminar

Mon, Apr 1 - Fri, Apr 5 2024
The 5-day OWM Volume Metrology Seminar is designed to enable metrologists to apply fundamental measurement concepts to

5856 Volume Metrology Seminar

Mon, Apr 8 - Fri, Apr 12 2024
The 5-day OWM Volume Metrology Seminar is designed to enable metrologists to apply fundamental measurement concepts to

Awards

Press Coverage

The Deprecation of the US Survey Foot

The American Surveyor
Some of you know about the deprecation of the U.S. survey foot already, and some may be asking “What the heck is deprecation?” So let’s start with a definition:

Contacts