The Stefan-Boltzmann constant (also Stefan's constant), a physical constant denoted by the Greek letter σ, is the constant of proportionality in the Stefan-Boltzmann law: the total energy radiated per unit surface area of a black body in unit time is proportional to the fourth power of the thermodynamic temperature.

The value of σ is 5.670 400(40) W·m^-2·K^-4. This value is derivable as well as experimentally determinable; see Stefan-Boltzmann law.

σ can be defined in terms of the Boltzmann constant $k\_\{\backslash mathrm\; B\}$ as:

$\backslash sigma\; =\; \backslash frac\{2\backslash pi^5k\_\{\backslash mathrm\; B\}^4\}\{15h^3c^2\}\; =\; \backslash frac\{\backslash pi^2k\_\{\backslash mathrm\; B\}^4\}\{60\backslash hbar^3c^2\},$

where h is Planck's constant, $\backslash hbar\; =\; h/2\backslash pi$is Dirac's form of Planck's constant, and c is the speed of light in a vacuum.

A related constant is the radiation constant (^*) which is equal to:

$\backslash frac\{4\backslash sigma\}\{c\}$

Physical constants

Constante de Stefan-Boltzmann | シュテファン＝ボルツマン定数 | Constante van Stefan-Boltzmann | Stefanova konstanta