# 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

[itex]\sigma = \frac{2\pi^5k^4}{15h^3c^2} = \frac{\pi^2k^4}{60\hbar^3c^2},[itex]

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