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The kilogram (kilogramme, $kg$) is a unit of mass. It is $1000$ grams (grammes, $g$).
One kilogram may soon be defined to be the mass of $N$ atoms of the carbon? isotope $\mathrm{C}^{12}$, where $N$ is $\frac{1000}{12}$ times the Avogadro number. Currently, however, this fact is actually the definition of the Avogadro number; instead, the kilogram is defined as the mass of a certain physical object kept by the BIPM in Paris.