Stefan Boltzmann Law Calculator
Calculate thermal radiation power from emissivity, area and temperature.
Stefan-Boltzmann Formula
P = εσAT⁴.
Understanding the Stefan-Boltzmann Law
The Stefan-Boltzmann law estimates total thermal radiation emitted by a surface from its temperature, area and emissivity. A perfect blackbody has emissivity 1, while real surfaces emit a fraction of that ideal amount.
Example Calculation
A blackbody surface of 1 m² at 500 K radiates about σ × 500⁴ = 3,544 W. A surface with emissivity 0.8 would emit about 80% of that value under the same conditions.
Factors and Interpretation
Temperature has a very strong effect because it is raised to the fourth power. Doubling absolute temperature increases ideal emitted power by a factor of 16. The calculator gives total emitted power, not net heat exchange with surrounding objects.
Frequently Asked Questions
Why must temperature be in kelvin?
The T⁴ relation requires absolute temperature.
What is emissivity?
It is a dimensionless measure from 0 to 1 describing how efficiently a real surface emits thermal radiation compared with a blackbody.
Does this include radiation from the surroundings?
No. Net radiative heat transfer requires subtracting incoming environmental radiation.
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Formula and Practical Limits
The Stefan–Boltzmann law gives ideal blackbody radiative power proportional to absolute temperature to the fourth power. Real surfaces require emissivity, and net heat transfer also depends on the surroundings.