Will a kilogram always equal a kilogram? This unit of mass (kg symbol) is, since May 20, 2019, defined from the Planck constant and no longer from a physical object. It's at the 26the meeting of the General Conference on Weights and Measures (GFCM) held in 2018 that the revision of the International System of Units (SI) had been determined.
Indeed, since 1889, the kilogram was equal to the mass of an iridized platinum cylinder (the famous prototype also called the
large K
) which was kept in Sèvres on the premises of the International Bureau of Weights and Measures (BIPM).
It is in particular in order to have a uniform IS accessible throughout the world in many sectors of activity (international trade, high-tech industry, human health...) but also to have units of measurement stable over the long term that the kilogram has been redefined.
Please note
As part of this 26e GFCM, the definitions of ampere, kelvin and mole have also been revised.
