Where does this come from, and can I check it?

One metre equals the distance light travels in vacuum during a tiny fraction of a second. 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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The metre is defined by the speed of light in vacuum

One metre equals the distance light travels in vacuum during a tiny fraction of a second

Historically based on a physical platinum-iridium bar in Paris, the International System of Units redefined the standard metre in 1983. It is currently defined as the path length light travels in a vacuum during a time interval of roughly one three-hundred-millionth of a second. Tying base units to fundamental physical constants ensures universal precision across laboratories.

Where this comes from

NIST

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Tags: measurement, si units, metre

The metre is defined by the speed of light in vacuum: the short answers

Where does this come from, and can I check it?: One metre equals the distance light travels in vacuum during a tiny fraction of a second. 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.