M_e = σ T⁴

where σ is the Stefan-Boltzmann constant and T is the thermodynamic temperature

Note 1 to entry: The Stefan-Boltzmann constant can be calculated by ${\displaystyle \sigma =\frac{2{\pi }^5{k}^4}{15h^3{c}_0^2}}$ where h is the Planck constant, c₀ is the speed of light in vacuum, and k is the Boltzmann constant.

Note 2 to entry: For the value of the Stefan-Boltzmann constant, σ, see CODATA.

Note 3 to entry: This entry was numbered 845-04-07 in IEC 60050-845:1987.