General Conference on Weights and Measures

The General Conference on Weights and Measures is the diplomatic body that adopts resolutions on the International System of Units and oversees the international framework for measurement.

International System of Units: The internationally agreed system of units built around seven base units and their derived units. The Conference adopts and revises the SI’s definitions and rules.
Metre Convention: The 1875 treaty establishing international cooperation on measurement and creating permanent metrology institutions. Its signatories established the institutions from which the Conference emerged.
Metrology: The science of measurement, including its methods, standards, uncertainty, and traceability. The Conference provides metrology with an international system of agreed units.
2019 redefinition of the SI base units: The 2019 revision that defined all seven SI base units through fixed values of fundamental constants. The Conference approved the shift from artifact-dependent definitions to fixed constants.
Carlos Ibáñez e Ibáñez de Ibero: A Spanish geodesist and statesman who became the first president of the International Committee for Weights and Measures. His leadership helped establish the new international metrology institutions after the Metre Convention.
International Committee for Weights and Measures: The elected committee that directs the work of the international measurement organization between General Conference meetings. It prepares technical matters and recommendations for the Conference.
International Prototype of the Metre: A platinum-iridium bar that served as the international reference for the metre from 1889 until 1960. Its adoption exemplified the physical-standard era shaped by early Conference decisions.
National measurement institute: A national organization responsible for maintaining measurement standards and supporting traceability within its country. National institutes implement and disseminate standards aligned with Conference decisions.
Planck constant: A fundamental constant relating a photon’s energy to its frequency and governing quantum scales. Fixing its value made the kilogram independent of the international prototype.
Henri Tresca: A French mechanical engineer who contributed to nineteenth-century metrology and served on international measurement bodies. His technical work connected early metric standards to the Conference’s institutional beginnings.

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