What is Legal Metrology?

Is it Legal Metrology or Weights and Measures?

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In the U.S., legal metrology is very closely related to the concept of weights and measures, which is the documentary standard infrastructure that specifies how technical artifacts and devices are to be used, together with the metrological performance criteria required, to test and verify regulated measuring instruments. Together, the systems of 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 protect the general public from deceptive measurement-related practices and provide confidence in our day-to-day business and consumer-based activities, such as fueling up your electric vehicle at a public EV charging station.

One of the largest differences between legal metrology and weights and measures may also 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 ties in with a State's weights and measures divisions but, in many cases, is separately managed as a distinct State laboratory metrology program. Please see the current directories of both the State Weights and Measures Directors and State Metrology Laboratories for more information regarding the state-by-state programs and organization.  

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.

How is NIST OWM Involved? 

A primary component of NIST OWM’s mission is to provide uniform legal metrology products and services to all states. However, the U.S. is unique in that its national-level office (i.e., OWM) does not maintain a national-level legal metrology system, nor is its function regulatory-based. 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.

OWM is active in legal metrology applied to commercial transactions. For example, this would include the regulated measuring instruments used in trade, such as grocery store scales, gasoline fuel pumps, and electric vehicle supply equipment (i.e., EV charging devices). 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.

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