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, as per the Stefan-Boltzmann law.

Its value is 5.670 400(40) × 10^-8 J s^-1 m^-2 K^-4.

The Stefan-Boltzmann constant can be defined in terms of the Boltzmann constant k by

<math>\sigma = \frac{2\pi^5k^4}{15h^3c^2} = \frac{\pi^2k^4}{60\hbar^3c^2},<math>

where h is Planck's constant, ħ is h-bar, and c is the speed of light.