As of the 2019 redefinition of SI base units, which establishes exact fixed values for k, h, and c, the Stefan–Boltzmann constant is exactly: σ σ = [ 2 π π 5 ( 1.380 649 × × 10 − − 23 ) 4 15 ( 2.997 924 58 × × 10 8 ) 2 ( 6.626 070 15 × × 10 − − 34 ) 3 ] W m 2 ⋅ ⋅ K 4 Thus,