Stefan Boltzmann Law Calculator

What Is the Stefan-Boltzmann Law?

The Stefan-Boltzmann law states that a perfect blackbody radiates power proportional to the fourth power of its absolute temperature. Real surfaces radiate less depending on emissivity. The law links temperature, area, and thermal radiation in physics and engineering.

Stefan-Boltzmann Formula

\(P\) is radiated power in watts, \(\varepsilon\) is emissivity (0 to 1), \(\sigma = 5.67 \times 10^{-8}\,\text{W/(m}^2\text{·K}^4)\), \(A\) is surface area in m², and \(T\) is absolute temperature in kelvin.

Example: \(\varepsilon = 0.9\), \(A = 1\,\text{m}^2\), \(T = 300\,\text{K}\) gives \(P \approx 413\,\text{W}\).

Emissivity and Temperature

A polished metal has low emissivity and radiates less than a matte black surface at the same temperature. Always convert Celsius to kelvin before applying the formula: \(T_\text{K} = T_\text{°C} + 273.15\).

Related tools: Blackbody Radiation Calculator and Blackbody Radiation Calculator.