Stefan-Boltzmann Law Calculator
Calculate radiant power from temperature using the Stefan-Boltzmann law.
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Enter the temperature in kelvin, the surface area in m2, and the emissivity (0 to 1, where 1 is a perfect blackbody). The calculator shows the total radiant power and power density.
About Stefan-Boltzmann Law
The Stefan-Boltzmann law, discovered independently by Josef Stefan (1879) and Ludwig Boltzmann (1884), describes the total power radiated by a thermal emitter. The power is proportional to the fourth power of absolute temperature, the surface area, and the emissivity. The Stefan-Boltzmann constant sigma = 5.67 x 10^-8 W/(m2 K4). This law is fundamental in astrophysics (stellar luminosity), climate science (Earth's energy balance), and engineering (furnaces, thermal management).
Frequently Asked Questions
What is the Stefan-Boltzmann law?
The Stefan-Boltzmann law states that the total radiant power emitted by a body is proportional to the fourth power of its absolute temperature: P = epsilon sigma A T^4.
What is emissivity?
Emissivity is a measure of how effectively a surface emits thermal radiation compared to a perfect blackbody. It ranges from 0 (perfect reflector) to 1 (perfect emitter/blackbody).
Why does power depend on T to the fourth?
The T^4 dependence means small temperature increases produce large increases in radiation. Doubling the absolute temperature increases radiated power by a factor of 16.