Stefan–Boltzmann Law Calculator (Radiated Power)
Enter the surface temperature, area and emissivity.
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Stefan–Boltzmann Law Calculator (Radiated Power) by TheCalcTools
How the Stefan–Boltzmann Law Calculator (Radiated Power) works
Every surface radiates power proportional to the fourth power of its absolute temperature: P = εσAT⁴, with σ = 5.670374419 × 10⁻⁸ W/(m²·K⁴).
A surface also absorbs radiation from its surroundings, so the net loss is εσA(T⁴ − T_surroundings⁴). Emissivity ranges from near 0 for polished metal to near 1 for a black body.
The formula
Worked example
Using the default values shown in the calculator:
| Surface temperature (°C) | 100 |
|---|---|
| Surroundings temperature (°C) | 20 |
| Area (m²) | 1 |
| Emissivity (0 to 1) | 0.95 |
- A 1 m² surface at 100 °C with emissivity 0.95 in a 20 °C room loses 646.6 W by radiation.
Result:
| Net radiated power (W) | 646.6 |
|---|---|
| Emitted power (W) | 1,044.4 |
| Emitted power per m² (W/m²) | 1,044.4 |
Frequently asked questions
Why does doubling the temperature matter so much?
Because of the fourth power: twice the absolute temperature means 16 times the radiated power.
Sources and further reading
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