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Stefan-Boltzmann Calculator — Thermal Radiation Heat Flux
Calculate net radiative heat flux between a gray surface and large surroundings from emissivity and absolute temperatures.
Last updated: September 17, 2026
Results
Use emissivity 0–1 and positive Kelvin temperatures
Formula, example and assumptions
qʺ=εσ(Ts⁴−Tsur⁴).
For ε=0.9, Ts=500 K and surroundings at 300 K, net flux is about 2.78 kW/m².
- Temperatures must be absolute Kelvin.
- Large-surroundings gray-surface approximation; view factor is treated as one.
Frequently asked questions
What does the Stefan-Boltzmann Calculator calculate?
Calculate net radiative heat flux between a gray surface and large surroundings from emissivity and absolute temperatures.
Which units should I use?
The input labels show the required SI units. Keep properties and geometry consistent before using the result in another engineering calculation.
Can I use this result for design?
Use it for transparent engineering estimates and checks. Validate property data, geometry, correlations and applicable codes for safety-critical design.