International metrology is established through coordination of activities between the NMIs of individual countries. A brief explanation of the main organisations within in the International Metrology scene is provided below. 

National Metrology Institute (NMI)

An NMI is an institute designated by national decision to develop and maintain national measurement standards for one or more quantities.

An NMI represents the country internationally in relation to the NMIs of other countries, in relation to the Regional Metrology Organisations and to the Bureau International des Poids et Mesures (BIPM). NMIs are the backbone of the international metrology organisations.

Some countries have a single organisation as the NMI (e.g. NIST, the National Institute of Standards and Technology, is the NMI of the USA), whereas other countries have a more distributed system. In the UK there are four laboratories which make up the NMI (the four NMS laboratories). NPL is main UK NMI laboratory and maintains the majority of the measurement standards in the UK. In addition:

• LGC maintains some of the chemical and biochemical standards.
• NEL maintains standards of flow.
• NMO, an Executive Agency of the Department for Business, Innovation and Skills, is responsible for managing and developing the National Measurement System and is also responsible for legal metrology.

Each of the four UK NMI laboratories represents the UK internationally in their respective technical areas. However in some circumstances (e.g. at the highest level of metrology such as the Metre Convention or the CIPM MRA) a single laboratory is required to represent the NMI in that country and in such cases this role is undertaken by NPL.

Visit the BIPM website to find links to other NMIs around the world.

BIPM and CIPM

Recognising the need to work towards internationally agreed measurement standards, in 1875 governments from 17 countries worldwide signed this treaty and agreed to create and finance a permanent, scientific institute, the BIPM, as the centre for coordination of world measurement. The central coordination role for worldwide metrology is undertaken by the BIPM with individual countries represented by NMIs. The Comité International des Poids et Mesures (CIPM) was established to oversee the BIPM and today there are 51 Member States of the Metre Convention, and 23 Associate States and Economies of the General Conference.

Regional Metrology Organisation (RMO)

NMIs from the same part of the world are often members of a RMO, which coordinates activities between its members and also between other RMOs.

The RMO for European NMIs is EURAMET and NPL is an active member of this organisation

A key activity in support of the international metrology system is international intercomparisons, which are undertaken both between the National Metrology Institutes and Designated Institutes from countries with the same RMO and also linking across different RMOs.

Find out more about international intercomparisons.