International Committee for Weights and Measures

The International Committee for Weights and Measures (CIPM) is an international body that promotes worldwide uniformity in units and advises on measurement standards under the Metre Convention.

Metre Convention: An 1875 treaty establishing international cooperation on measurement and the institutions that maintain the International System of Units. The convention established the CIPM and defines its role in international measurement governance.
International Prototype of the Kilogram: A platinum-iridium cylinder that served as the international reference for the kilogram from 1889 to 2019. The CIPM’s early institutional work included overseeing this shared physical mass standard.
CIPM membership: The committee’s limited membership of experts appointed under the Metre Convention’s institutional framework. Membership determines who deliberates and advises on the committee’s technical and governance questions.
Key comparison: An international measurement comparison used to test and document the equivalence of national standards. Comparisons organized under the CIPM framework help demonstrate that national results agree.
International Bureau of Weights and Measures: An intergovernmental organization that coordinates international measurement standards and maintains reference standards. The CIPM supervises this bureau, which carries out much of the convention’s technical work.
International Prototype of the Metre: A platinum-iridium bar adopted in 1889 as the international reference for the metre. The prototype illustrates the physical standards managed through the system the CIPM helped administer.
National metrology institute: A national organization responsible for realizing, maintaining, or disseminating measurement standards. CIPM members often bring expertise and institutional ties from national metrology systems.
Measurement uncertainty: A quantified parameter describing the dispersion of values reasonably attributable to a measured quantity. Shared standards and comparisons make uncertainty estimates more meaningful between laboratories.
General Conference on Weights and Measures: The Metre Convention’s member-state body, which meets periodically to decide major questions of measurement standards. The conference elects CIPM members and receives its reports.
Metric system: A decimal system of measurement units that developed in France and became the basis of the modern SI. The drive to coordinate metric standards internationally preceded the committee’s creation.

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