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.