Stefan-Boltzmann constant

The Stefan-Boltzmann constant (also Stefan's constant), denoted with a Greek letter σ, is a derivable physical constant, the constant of proportionality between the total energy radiated per unit surface area of a black body in unit time and the fourth power of the thermodynamic temperature. Its value is 5.670 400(40) × 10^-8 J s^-1 m^-2 K^-4. See also Stefan-Boltzmann law.