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Compute thermal radiation from a blackbody/grey body (Stefan-Boltzmann law): blackbody emissive power E_b = σ·T⁴ (W/m²), total radiated power Q_rad = ε·σ·A·T⁴ (W); with an optional surrounding temperature T₀ it also computes the net radiative exchange Q_net = ε·σ·A·(T⁴-T₀⁴) (W). σ = 5.670374419e-8 W/(m²·K⁴); ε is the emissivity (0 < ε ≤ 1, blackbody ε=1); T is the ABSOLUTE temperature (K) — °C and °F are first converted to K (this is an absolute temperature, not a difference); A is the radiating area. Area in m²/cm².
Execution
Fill in the form, run the tool, and review the result in one place.
Samples
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Tool usage guide
The Heat Radiation Calculator uses the Stefan-Boltzmann law to calculate blackbody emissive power, total radiated power, and optional net radiative exchange. Enter emissivity, absolute temperature, and radiating area, with temperature available in K, °C, or °F and area in m² or cm².
Background
A student needs the radiation output of an ideal blackbody surface at 300 K.
Problem
Find the emissive power and total radiated power for a 1 m² surface.
How to use
Set emissivity to 1, temperature to 300 K, area to 1 m², and choose 4 decimal places.
ε = 1; T = 300 K; A = 1 m²Outcome
The calculator returns E_b = 459.3003 W/m² and Q_rad = 459.3003 W.
Background
An analyst is evaluating a grey surface operating at 100°C in surroundings at 27°C.
Problem
Calculate both the surface's total radiated power and its net radiative exchange.
How to use
Enter emissivity 0.8, surface temperature 100°C, area 0.5 m², and surrounding temperature 27°C.
ε = 0.8; T = 100 °C; A = 0.5 m²; T₀ = 27 °CIt calculates blackbody emissive power E_b, total radiated power Q_rad, and optional net radiative exchange Q_net.
The calculator uses E_b = σT⁴, Q_rad = εσAT⁴, and, when T₀ is provided, Q_net = εσA(T⁴ − T₀⁴).
Yes. Select °C or °F, and the calculator converts the absolute temperature to Kelvin before calculating.
Enter ε = 1 for an ideal blackbody. Grey surfaces use an emissivity greater than 0 and no greater than 1.
The calculator returns blackbody emissive power and total radiated power, while net radiation is not calculated.
Outcome
The calculator returns E_b = 1099.3741 W/m², Q_rad = 439.7497 W, and Q_net = 255.6618 W.