Stefan-Boltzmann constant

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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)×10⁻⁸ 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_] as:

[\sigma = \frac^4} = \frac^4},]

where h is Planck's constant, [\hbar = h/2\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 ([link]) which is equal to:

[\frac]

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