[nerdponx]

Why is the kilogram the base unit and not the gram?

[FabHK]

Good question. Apparently, the unit (mass of 1 litre of water at the ice point) was supposed to be called "grave", but then it was considered that most measurements would be for much smaller amounts, and so it was switched to the gramme, but then for the definition they stuck to the original idea, now re-christened kg.

I don't quite understand this, as they could've defined it to be the mass of one cubic centimetre of water, rather than a cubic decimetre of water. Or they could've said that the unit is gram, and 1 g is 1/1000 of the mass of this artefact.

I've also read stories that revolutionaries objected to the name "grave", as it is close to Grave (French), Graf (German), that is, the title of nobility (anathema for the Republicans of the French Revolution). Thus, instead of 1 grave we have 1 kilogram.

At any rate, it was all rather messy and political, as the delightful book Whatever Happened to the Metric System?: How America Kept Its Feet by John Bemelmans Marciano recounts.

See also precisely this question at Physics StackExchange:

https://physics.stackexchange.com/questions/64562/why-metric...

[mamon]

Because it was easier to produce prototype of a bigger unit? And easier to measure it with lower error margin?

[pdonis]

Because of how SI units evolved historically; basically, there was the "cgs" version of the metric system, and the "mks" version, and the latter won out. (Note that neither version has all three "base" units pure in terms of metric prefixes--the first has centimeters instead of meters, the second has, as you note, kilograms instead of grams.)