https://doi.org/10.1351/goldbook.K03391
The kilogram, symbol \(\text{kg}\), is the SI unit of mass. It is defined by taking the fixed numerical value of the @P04685@ \(h\) to be \(6.626\ 070\ 15\times 10^{-34}\) when expressed in the unit \(\text{J s}\), which is equal to \(\text{kg}\ \text{m}^{2} \text{s}^{-1}\), where the metre and the second are defined in terms of @S05854-1@ and @S05854-2@.
Source:
BIPM, The International System of Units, SI Brochure, 9th ed. (2019), p. 131 [Terms] [Book]