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 following are a series of Frequently Asked Questions (FAQs) that are related to weights and measures, the Metric (SI) program, and legal metrology.
If you don't find the answer to your question on these pages, send us an email at owm [at] nist.gov (owm[at]nist[dot]gov)
All countries have recognized and adopted the SI, including the United States. There are still countries that are amending their national laws to adopt a mandatory metric policy and others pursuing voluntary metrication. From a technical perspective, it’s impossible to avoid using the metric system as all measurement units (including non-SI or U.S. customary units) are defined in terms of the SI. The NIST blog article, Busting Myths about the Metric System, discusses some common misconceptions about the status of U.S. metrication. Learn more about U.S. Metrication and explore these Metrication FAQs for additional information.
These are uniform (i.e., representing all stakeholders) documentary standards that are critical to consumer protection, economic growth and trade. They help ensure that consumers get what they pay for and that sellers get fair payment for the goods and services they provide.
These published standards provide technical rigor (e.g., technical specifications, test procedures and labeling requirements) when weighing and measuring products and services for sale, such as a pound of beef, a gallon of gasoline, or a mile driven in a taxicab.
As a non-regulatory Federal agency, NIST does not regulate the use of weights and measures. Weights and measures are regulated by the States. However, through the NIST Organic Act, Congress authorized NIST to cooperate with the States in securing uniformity in weights and measures laws and methods of inspection.
NIST doesn’t set standards itself. The documentary standards that NIST publishes are developed via a consensus process that involve all stakeholders. The U.S. standards development system is voluntary, decentralized, consensus-based, and driven by public sector needs. NIST does not decide to which standards are developed and/or published.
NIST brings together stakeholders, provides technical guidance, and facilitates the process to develop the standards. NIST is responsible for the overall content, interpretation, and maintenance of these standards as published through NIST and the Department of Commerce.
Legal Metrology refers to the system of laws that are used to regulate measuring instruments used in trade and commerce (such as grocery store scales and gasoline pumps) whereas Weights and Measures generally specifies the usage and performance of these devices that are used to test regulated measuring instruments. Learn more about this topic here...