# International Bureau of Weights and Measures

The International Bureau of Weights and Measures (French: Bureau International des Poids et Mesures, BIPM) is an intergovernmental organisation, through which its 64 member-states act on measurement standards in areas including chemistry, ionising radiation, physical metrology, as well as the International System of Units (SI) and Coordinated Universal Time (UTC). It is based in Saint-Cloud, near Paris, France. The organisation has been referred to as IBWM (from its name in English) in older literature.

## Structure

The BIPM is overseen by the International Committee for Weights and Measures (French: Comité international des poids et mesures, CIPM), a committee of eighteen members that meet normally in two sessions per year, which is in turn overseen by the General Conference on Weights and Measures (French: Conférence générale des poids et mesures, CGPM) that meets in Paris usually once every four years, consisting of delegates of the governments of the Member States and observers from the Associates of the CGPM. These organs are also commonly referred to by their French initialisms.

## History

The BIPM was created on 20 May 1875, following the signing of the Metre Convention, a treaty among 17 Member States. As of December 2024, there are now 64 members.
It is based at the Pavillon de Breteuil in Saint-Cloud, France, a 4.35 ha (10.7-acre) site (originally 2.52 ha or 6.2 acres) granted to the Bureau by the French Government in 1876. Since 1969 the site has been considered international territory, and the BIPM has all the rights and privileges accorded to an intergovernmental organisation. This status was further clarified by the French decree No 70-820 of 9 September 1970.
Several significant changes to the BIPM have been made throughout its history during the meetings overseen by the CGPM. An example of this would be how in the 12th general council meeting (held in 1964), the BIPM's budget was increased from $300,000 to $600,000 per year. A historic moment for the BIPM occurred during the 26th CGPM in 2018. At this council, it was decided that world standard for the units of kilograms, seconds, amperes, Kelvins, moles, candelas, and meters would be redefined to reflect constants in nature. This is the first time this has happened since the creation of the BIPM. These changes were made official on World Metrology Day in 2019.
Beginning in 1970, the BIPM began publishing the SI Brochure, a document detailing an up-to-date version of the International System of Units. As of December 2024, the most recent version of the SI Brochure was the 9th edition published in 2019.

## Function

The BIPM has the mandate to provide the basis for a single, coherent system of measurements throughout the world, traceable to the International System of Units (SI). This task takes many forms, from direct dissemination of units to coordination through international comparisons of national measurement standards (as in electricity and ionising radiation).
Following consultation, a draft version of the BIPM Work Programme is presented at each meeting of the General Conference for consideration with the BIPM budget. The final programme of work is determined by the CIPM in accordance with the budget agreed to by the CGPM.
Currently, the BIPM's main work includes:
* Making brochures that define the International System of Units.
* Scientific and technical activities carried out in its four departments: chemistry, ionising radiation, physical metrology, and time
* Liaison and coordination work, including providing the secretariat for the CIPM Consultative Committees and some of their Working Groups and for the CIPM MRA, and providing institutional liaison with the other bodies supporting the international quality infrastructure and other international bodies
* Capacity building and knowledge transfer programs to increase the effectiveness within the worldwide metrology community of those Member State and Associates with emerging metrology systems
* A resource centre providing a database and publications for international metrology
The BIPM is one of the twelve member organisations of the International Network on Quality Infrastructure (INetQI), which promotes and implements QI activities in metrology, accreditation, standardisation and conformity assessment.
The BIPM has an important role in maintaining accurate worldwide time of day. It combines, analyses, and averages the official atomic time standards of member nations around the world to create a single, official Coordinated Universal Time (UTC).

## Directors

Since its establishment, the directors of the BIPM have been:
| Name | Country | Mandate | Notes |
| Gilbert Govi | Italy | 1875–1877 | |
| J. Pernet | Switzerland | 1877–1879 | Acting director |
| Ole Jacob Broch | Norway | 1879–1889 | |
| J.-René Benoît | France | 1889–1915 | |
| Charles Édouard Guillaume | Switzerland | 1915–1936 | |
| Albert Pérard | France | 1936–1951 | |
| Charles Volet | Switzerland | 1951–1961 | |
| Jean Terrien | France | 1962–1977 | |
| Pierre Giacomo | France | 1978–1988 | |
| Terry J. Quinn | United Kingdom | 1988–2003 | Honorary director |
| Andrew J. Wallard | United Kingdom | 2004–2010 | Honorary director |
| Michael Kühne | Germany | 2011–2012 | |
| Martin J. T. Milton | United Kingdom | 2013–present | |