The international system of measurements has been overhauled with new definitions for the kilogram and other key units.
At a meeting in Versailles, France, countries have voted to approve the wide-ranging changes that underpin vital human activities like global trade and scientific innovation.
The most closely watched change was the revision to the kilo, the measurement of mass.
Until now, it has been defined as the mass of a platinum-iridium lump, the so-called Grand K, that is kept in a secured vault on the outskirts of Paris. It has been the world's one true kilo, against which all others were measured, since 1889.
It is now being retired and replaced by a new definition based on a scientific formula. In their vote, countries also unanimously approved updates to three other key units: the kelvin for temperature, the ampere for electrical current and the mole for the amount of a substance.
The vote was greeted by sustained applause and cheers, after the 50-plus countries in attendance said yes or oui when asked one by one for their decision.