Definition:Metric System/Mass/Kilogram

Definition
The kilogram is the SI base unit of mass.

It is defined as being equal to the mass of the International Prototype Kilogram (IPK) which is almost exactly equal to the mass of one liter of water.

The weight of the IPK has been known to vary, and so a more stable alternative is being sought, based on a fundamental constant. A decision is expected to be reached in 2011.

Symbol
The symbol for the kilogram is $\mathrm {kg}$.

Linguistic Note
The original British English spelling was kilogramme, but this is rarely used nowadays, as the American kilogram is now the international standard.

Also see

 * Definition:Gram