Definition:Metric System/Mass/Kilogram

Definition
The kilogram is the SI base unit of mass.

It is defined as being equal to:


 * The fixed numerical value of the Planck constant $h$ to be $6 \cdotp 62607015 \times 10^{-34}$ when expressed in the unit Joule seconds.

The Joule second is equal to $1 \, \mathrm {kg} \, \mathrm m^2 \, \mathrm s^{−1}$, where the metre and the second are defined in terms of:
 * the speed of light $c$
 * the time of transition between the two hyperfine levels of the ground state of the caesium $133$ atom at rest at $0 \, \mathrm K$.

Also see

 * Definition:Gram
 * Definition:Milligram