Stefan–Boltzmann constant

https://doi.org/10.1351/goldbook.S05964
Fundamental physical constant \(\sigma = \frac{2\ \pi ^{5}\ k^{4}}{15\ h^{3}\ c_{0}^{2}} = 5.670\ 51(19)\times 10^{-8}\ \rm{W}\ \rm{m}^{-2}\ \rm{K}^{-4}\).
Source:
CODATA Bull. 1986, 63, 1 [Terms] [Book]