= Kilogram
{title2=$\mathrm{kg}$}
The <kilogram> is the SI base <unit of mass>. The modern definition fixes the numerical value of <Planck constant> to $h=6.62607015\times10^{-34}\,\mathrm{J\,s}$, 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.<The International System of Units (SI), ninth edition, SI Brochure>[§2.3.1, kilogram definition]{ref}
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