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Base mass units no longer depend on physical metal artifacts stored in vaults. The figure is taken from NIST, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.

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Mondo Knows Facts

The kilogram was redefined in 2019 using Planck's constant

Base mass units no longer depend on physical metal artifacts stored in vaults

For over a century, the kilogram was defined by the mass of a single cylinder of platinum-iridium kept in France. In May 2019, the International Bureau of Weights and Measures redefined the kilogram by fixing the numerical value of Planck's constant using precision Kibble balance scales. This change ensures the mass standard stays permanent and reproducible anywhere.

Where this comes from

NIST

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Tags: measurement, si units, kilogram

The kilogram was redefined in 2019 using Planck's constant: the short answers

Where does this come from, and can I check it?: Base mass units no longer depend on physical metal artifacts stored in vaults. The figure is taken from NIST, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
Is this really a science fact?: Yes. It sits on the Science shelf, one of 1,090 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
What else can I read about it?: The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.