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

Metre, kilogram, second, ampere, kelvin, mole and candela anchor every measure. The figure is taken from BIPM, 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 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.

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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.

Mondo Knows Facts

The SI rests on seven base units

Metre, kilogram, second, ampere, kelvin, mole and candela anchor every measure Every other SI unit is built from combinations of these seven. Since 2019 all of them are defined by fixed values of physical constants rather than by physical objects. The kilogram, for instance, is now set by the Planck constant. It sits in Mondo's science collection, one of 200 facts that each trace back to the reference below.

Where this comes from

BIPM

Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.

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More facts like this

SI prefixes scale measurements by powers of tenKilo multiplies by a thousand and milli divides by the same amount Standard gravity is fixed at 9.80665The agreed value describes free fall at sea level and 45 degrees latitude Minus forty is the same in both scalesThe Celsius and Fahrenheit scales meet at exactly minus 40 degrees The Beaufort scale describes wind by its effectsTwelve steps run from calm air to a hurricane, once judged by the canvas a ship carried Lavoisier showed that mass is conservedWeighing sealed reactions proved that nothing vanishes in combustion The metre is defined by the speed of light in vacuumOne metre equals the distance light travels in vacuum during a tiny fraction of a second

Tags: measurement, units, si

The SI rests on seven base units: the short answers

Where does this come from, and can I check it?: Metre, kilogram, second, ampere, kelvin, mole and candela anchor every measure. The figure is taken from BIPM, 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 2,600 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.