The unit of weight in the metric system; accepted as the unit of
mass in the absolute of C. G. S. system of units. It is the
one-thousandth part of mass of a standard weight preserved under proper
conditions in Paris, and supposed to be the mass of a cubic decimeter of
distilled water at the temperature of the maximum density of water. The
standard is the kilogram; the temperature is 3.9º C. (39º F.). The
standard kilogram is found to be not exactly the weight of a cubic
decimeter of water, the latter weighing 1.000013 kilogram.

If therefore the defined gram on the water basis is taken as the unit it
varies very slightly from the accepted gram.

1 gram is equal to 15.43234874 grains. (Prof. W. H. Miller.)