Kilogram ( $kg$ )

The kilogram is the SI base unit of mass. The modern definition fixes the numerical value of Planck constant to

h = 6.62607015 \times 1 0^{- 34} J s

, with the metre and second defined through the other SI constants. It is no longer defined by the mass of a particular metal artifact.

A realization connects the defining constant to a practical mass measurement. That experiment has uncertainty even though the constant's defining numerical value is exact. The gram and milligram are decimal submultiples of the kilogram.^[ref]

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A kilogram (kg) is a unit of mass in the International System of Units (SI). It is defined as being equal to the mass of the International Prototype of the Kilogram, a platinum-iridium cylinder that was kept at the International Bureau of Weights and Measures (BIPM) in France.

Unit of mass.

Defined in the 2019 redefinition of the SI base units via the Planck constant. This was possible due to the development of the Kibble balance.