The Stefan–Boltzmann constant (also Stefan's constant), a physical constant denoted by the Greek letter σ (sigma), is the constant of proportionality in the Stefan–Boltzmann law: "the total intensity radiated over all wavelengths increases as the temperature increases", of a black body which is proportional to the fourth power of the thermodynamic temperature. The value of the Stefan–Boltzmann constant is given in SI units by:
σ = 5.670367(13)×10−8 W⋅m−2⋅K−4
