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Legal Metrology

What is Legal Metrology...and how is it different from Weights and Measures?

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. This is very closely related to the concept of Weights and Measures, which is the metrology infrastructure that specifies the usage and performance of technical artifacts and devices that are used to test and verify the regulated measuring instruments. Together, Legal Metrology and Weights and Measures promote uniformity in laws and regulations and ensure equity in trade and commerce. In other words, these underlying systems protects the general public from deceptive measurement-related practices and provides confidence to our day-to-day business activities.

image of scales and Legal Metrology system of laws that are used to regulate measuring instruments used in trade and commerce

A primary component of NIST OWM’s mission is to provide uniform legal metrology products and services to all the states. However, the U.S. is rather unique in that its national-level office (i.e., OWM) does not maintain a national level legal metrology system nor is its function a regulatory-based one. Rather, the legal metrology products and services that OWM provides are voluntarily and individually adopted by the States and other local jurisdictions, which are then responsible for the day-to-day regulatory function of the U.S. Weights and Measures system.

Photo of electric vehicle charging and definition of weights and measures

NIST OWM is also responsible for the Legal Metrology function for the U.S via a diplomatic treaty with the international metrology community (see OIML). Likewise, our legal metrology function is directly aligned with NIST’s activities as the National Metrology Institute (NMI) for the U.S. to advance measurement science, standards, and technology and promote equitable standards worldwide, as well as our NIST mission to promote U.S. innovation and industrial competitiveness to enhance economic security.

One of the largest differences between Legal Metrology and Weights and Measures may reside in a practical, laboratory realization of the SI with fundamental physical measurements (mass, length, and volume). Within the U.S. (i.e., states, territories, and local jurisdictions), this practice is commonly referred to as Weights and Measures. To add to the complexity, this may be referred to as both Legal Metrology and Weights and Measures within the international metrology community. For example, the International Bureau of Weights and Measures (BIPM) and the International Bureau of Legal Metrology (BIML) work closely together to ensure that these concepts are realized in practice through both fundamental measurements and documentary standards that directly support global trade and commerce.


Created March 10, 2023, Updated July 24, 2023