What is the Stefan-Boltzmann constant?

The Stefan-Boltzmann constant (σ) is 5.670374419 × 10⁻⁸ W m⁻² K⁻⁴. It relates the total energy radiated per unit surface area of a blackbody to the fourth power of its absolute temperature.

What does emissivity mean?

Emissivity (ε) is a dimensionless ratio from 0 to 1 describing how efficiently a surface radiates energy compared to a perfect blackbody. A value of 1 is a perfect blackbody; polished metals may be as low as 0.02.

Why must temperature be in Kelvin?

The Stefan-Boltzmann law uses absolute temperature (Kelvin) because the T⁴ relationship is derived from thermodynamic principles that require zero at absolute zero. The calculator converts Celsius and Fahrenheit to Kelvin automatically.

What is net radiation between two surfaces?

Net radiation is the difference between power emitted and power absorbed. For a surface at T₁ in an environment at T₂, net power = εσA(T₁⁴ − T₂⁴). This calculator computes gross emission; use the net mode for two-temperature scenarios.

What are typical emissivity values?

Blackbody (theoretical): 1.0. Human skin: ~0.98. Brick: ~0.90. Concrete: ~0.88. Polished aluminum: ~0.05. Polished copper: ~0.03. The calculator includes a preset list for common materials.

Stefan-Boltzmann Calculator

Name: Stefan-Boltzmann Calculator
Availability: InStock
Author: Nham Vu

Calculate thermal radiation power from a surface using the Stefan-Boltzmann law: P = εσT⁴A.

Input Parameters

Temperature

Temperature in Kelvin must be > 0.

Emissivity (ε) — 0 to 1

Surface Area

Net radiation mode

Subtract absorption from surroundings at ambient temperature.

Enter values and click Calculate to see results.

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Summary

Calculate thermal radiation power from a surface using the Stefan-Boltzmann law: P = εσT⁴A.

How it works

Enter the surface temperature in Kelvin (or switch to Celsius/Fahrenheit).
Set the emissivity value between 0 (perfect reflector) and 1 (perfect blackbody).
Enter the surface area in square meters.
The calculator applies P = εσT⁴A using σ = 5.670374419 × 10⁻⁸ W m⁻² K⁻⁴.
Results show radiated power in watts, kilowatts, and megawatts.

Use cases

Estimate heat loss from industrial furnaces and kilns.
Calculate stellar luminosity from surface temperature and radius.
Analyze thermal radiation in building energy audits.
Design radiative cooling systems for electronics.
Study climate and planetary energy balance.
Verify thermal sensor readings in engineering experiments.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu