General Conference on Weights and Measures (CGPM)

The General Conference on Weights and Measures—commonly abbreviated CGPM, from the French "Conférence générale des poids et mesures"—is the supreme decision-making body of the international system of measurement. It comprises delegations from countries that have joined the Metre Convention. The meetings are held periodically and take place in France.

The CGPM's function is to approve definitions of base units, to consider updates to the International System of Units (SI), and to endorse the budgets and procedures of the scientific bodies that work under it.

Structure of the bodies

The Metre Convention framework comprises three interconnected bodies. The CGPM is the intergovernmental decision-making body. The CIPM (International Committee for Weights and Measures) is an expert committee responsible for ongoing work and provides advice to the CGPM. The BIPM (International Bureau of Weights and Measures) is the research and testing centre, located in Sèvres near Paris. There are also advisory committees specializing in particular areas such as time, electrical measurement, and radiation.

Base units

The SI is built on seven base units: the metre (length), kilogramme (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity). All other units used in measurement are derived from these.

Changes to definitions

For a long time, some base units were defined by reference to physical objects—for example, the kilogramme was defined by a platinum standard kept at the BIPM. A major change occurred when definitions were revised to be based on natural constants, such as Planck's constant and the speed of light. This approach allows measurements to be reproduced at any location in the world without dependence on a particular artifact.