CGPMs

CGPMs, formally the Conférence générale des poids et mesures, is the supreme international body governing the International System of Units (SI). It was established by the Metre Convention of 1875 and serves as the highest authority for defining units, approving new standards, and endorsing reference materials and dissemination rules. The conference meets in plenary sessions roughly every four years at venues chosen by member states and issues resolutions that guide the work of the CIPM and the BIPM.

Membership and functions: The CGPM comprises delegates from signatory states and certain associate entities. Its resolutions define official unit definitions and symbols and authorize the dissemination of measurement standards. While it does not perform measurements itself, it sets policy and approves changes based on scientific advances.

Relationship to CIPM and BIPM: The CGPM delegates technical implementation to the International Committee for Weights and Measures (CIPM), which administers the SI through the BIPM, the permanent international metrology institute near Paris. The BIPM provides metrology services, maintains standards, and coordinates international comparisons.

Notable actions: At its 26th meeting in 2018, the CGPM approved redefining four SI base units—the kilogram, ampere, kelvin, and mole—by fixing fundamental constants (Planck constant h, elementary charge e, Boltzmann constant k, and Avogadro constant NA). The changes took effect on 20 May 2019, shifting the SI away from artifact-based definitions toward invariant constants to ensure long-term stability.