Sevres.science / Sèvres, the place

Conferences & Events

How a decision about units is made

Changes to the SI start with the specialists. Each consultative committee of the CIPM, for example for mass, for time and frequency or for thermometry, brings together national metrology institutes working in its field. When a committee is convinced that a change is ready, it recommends it to the CIPM.

The CIPM, eighteen metrologists from different countries, meets every year, oversees the work of the BIPM and reports to the General Conference. Only the General Conference, where the member states of the Metre Convention vote, can change the definition of a unit. That is how the 2018 vote that redefined the kilogram, ampere, kelvin and mole came about, how the 2022 decision on new prefixes was taken, and how in October 2026 the decision was made that UTC will run without leap seconds from 20 May 2027.

• Worldwide, every year on 20 May

  World Metrology Day

  Organised jointly by the BIPM and the International Organization of Legal Metrology (OIML), with national metrology institutes taking part. The date marks the signing of the Metre Convention in 1875. In November 2023 the UNESCO General Conference officially recognised the annual celebration.

  Official website →

• At least once every six years

  General Conference on Weights and Measures (CGPM)

  The meeting of the states of the Metre Convention, where decisions about the SI are taken. Under the Convention it meets at least once every six years.

  Official website →

• Sèvres, every September

  European Heritage Days in Sèvres

  The town and the national manufactory open their heritage to visitors. Check the town's and the manufactory's websites for the year's programme.

  Official website →