Source: NIST

SI multiples of gram
Multiple Name Symbol Multiple Name Symbol
100 gram g      
101 decagram dag 10–1 decigram dg
102 hectogram hg 10–2 centigram cg
103 kilogram kg 10–3 milligram mg
106 megagram Mg 10–6 microgram µg
109 gigagram Gg 10–9 nanogram ng
1012 teragram Tg 10–12 picogram pg
1015 petagram Pg 10–15 femtogram fg
1018 exagram Eg 10–18 attogram ag
1021 zettagram Zg 10–21 zeptogram zg
1024 yottagram Yg 10–24 yoctogram yg
caption This international prototype, made of platinum-iridium, is kept at the BIPM under conditions specified by the 1st CGPM in 1889. Photograph courtesy of © BIPM

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.

Further reading
The NIST Reference on Constants, Units, and Uncertainty

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(2007). Kilogram. Retrieved from


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