https://doi.org/10.1351/goldbook.K03374
The kelvin, symbol K, is the SI unit of thermodynamic temperature. It is defined by taking the fixed numerical value of the Boltzmann constant k to be 1.380 649×1023 when expressed in the unit J K1, which is equal to kgm2s2K1, where the kilogram, metre and second are defined in terms of h, c and ΔνCs.
Source:
BIPM, The International System of Units, SI Brochure, 9th ed. (2019), p. 133 [Terms] [Book]