Stefan-Boltzmann Radiation Calculator
Heat radiated by a hot surface, the net loss to its surroundings and the wavelength it peaks at.
Results
Power
18,235.15
W
Power
17,858.26
W
Heat flux
18,235.15
W/m²
Wavelength
3.7480
µm
What this tool does
Radiated power goes with the fourth power of absolute temperature, so doubling the temperature multiplies the heat by sixteen — which is why radiation dominates above a few hundred degrees and can be ignored below room temperature. Emissivity is close to 0.95 for paint, brick and skin, but as low as 0.05 for polished metal, which is exactly why insulation is shiny.
Formula
P = ε × σ × A × T⁴ (σ = 5,670 374 419 × 10⁻⁸ W/m²K⁴)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
t | Temperature | °C |
a | Area | m² |
em | Emissivity | — |
ta | Surrounding temperature | °C |
P | Power | W |
PN | Power | W |
PA | Heat flux | W/m² |
WL | Wavelength | µm |
Worked example
- Temperature500 °C
- Area1 m²
- Emissivity0.9
- Surrounding temperature20 °C
- Power18,235.15 W
- Power17,858.26 W
- Heat flux18,235.15 W/m²
- Wavelength3.7480 µm
Limitations
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- Temperatures below absolute zero (−273.15 °C) do not exist physically. The converter will still show the arithmetic result.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.