In an historic vote, nations unanimously approved Friday a groundbreaking overhaul to the international system of measurements, creating new definitions for the kilogram and other key units vital for trade and science.
Scientists for whom the update represents decades of work clapped, cheered and even wept as the 50-plus nations one by one said "yes" or "oui" to the update.
Nobel prize winner William Phillips said now it can be certain "that the kilogram is stable".
"We weren't sure of that in the past. And now we will be."
The so-called 'Grand K' kilogram, a cylinder of polished platinum-iridium alloy that has been the world's sole true kilo since 1889, is to be retired.
Nations gathered in Versailles, west of Paris, instead approved the use of a scientific formula to define the exact weight of a kilogram.
The change won't have an impact for most people - their bathroom scales won't get kinder and kilos and grams won't change in supermarkets.
Instead, "the immediate impacts, perhaps for the most parts impacts for the next decades, are going to be for scientific purposes", said Phillips.
It would also mean redundancy for the Grand K and its six official copies.
The new formula-based definition of the kilogram will have multiple advantages over the precision-crafted metal lump that has set the standard for more than a century.
Unlike a physical object the formula cannot pick up particles of dust, decay with time or be dropped and damaged.
"We future-proofed this system," said Martin Milton, director of Bureau International de Poids et Mesures. "We put in place a system that doesn't depend on something that is 140 years old."
It also is expected to be more accurate when measuring very, very small or very, very large masses.
"It's really hard to go from a kilogram to a milligram under the present system, but under the new system, a milligram is as straightforward to realise as a kilogram," said William Phillips, scientist and National Institute of Standards and Technology.