|SI multiples of gram|
The kilogram is the unit of mass in the International System of Units (SI). It is one of the seven SI base units. At the end of the 18th century, a kilogram was the mass of a cubic decimeter of water. In 1889, the 1st General Conference on Weights and Measures (CGPM) sanctioned the international prototype of the kilogram, made of platinum-iridium, and declared: This prototype shall henceforth be considered to be the unit of mass. The picture at the right shows the platinum-iridium international prototype, as kept at the International Bureau of Weights and Measures under conditions specified by the 1st CGPM in 1889.
The 3d CGPM (1901), in a declaration intended to end the ambiguity in popular usage concerning the word "weight," confirmed that:
The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.
The NIST Reference on Constants, Units, and Uncertainty
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