What is the Stefan-Boltzmann constant?

It is σ = 5.670374419 × 10⁻⁸ W·m⁻²·K⁻⁴. It relates the total radiated power per unit area of a blackbody to the fourth power of its absolute temperature.

What does emissivity mean?

Emissivity (ε) is a dimensionless value from 0 to 1 that measures how efficiently a surface radiates compared to a perfect blackbody. Polished metals are near 0.05; matte black paint is near 0.97.

Why does the calculator use T⁴?

The Stefan-Boltzmann law states that radiated power scales with the fourth power of absolute temperature. A small rise in temperature causes a large increase in radiation.

What is net radiated power?

Net power accounts for both emission and absorption from the surrounding environment. It equals P = εσA(T⁴ − T_amb⁴). When the body is cooler than its surroundings, the net value is negative (net absorption).

Does this apply to real objects?

Yes, with the emissivity factor. Real objects are "gray bodies" — they emit a fraction ε of what a perfect blackbody would at the same temperature. The formula is exact for uniform-temperature surfaces.

Stefan-Boltzmann Power Calculator

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

Enter surface area, emissivity, and temperature to compute total thermal radiation power via the Stefan-Boltzmann law.

Inputs

Surface Area (m²)

Emissivity (0 – 1)

Blackbody = 1.0 | Polished metal ≈ 0.05 | Matte black ≈ 0.97

Surface Temperature

Ambient Temperature (optional — for net power)

Results

Enter values and click Calculate

Common Emissivity Values

Material	Emissivity (ε)
Blackbody (ideal)	1.00
Human skin	0.98
Matte black paint	0.97
Brick / concrete	0.90
Oxidized steel	0.70
Anodized aluminum	0.55
Unpolished aluminum	0.12
Polished copper / silver	0.03

Click an emissivity value to fill the input field.

Summary

Enter surface area, emissivity, and temperature to compute total thermal radiation power via the Stefan-Boltzmann law.

How it works

Enter the surface area of the emitting body in square meters.
Set the emissivity (0 = perfect mirror, 1 = perfect blackbody).
Enter the surface temperature in Kelvin (or switch to Celsius/Fahrenheit).
Optionally enter an ambient temperature to compute net radiated power.
The calculator applies P = εσA(T⁴ − T_amb⁴) and displays the result in watts.

Use cases

Estimate heat loss from a furnace or industrial oven.
Calculate radiated power from a star given radius and temperature.
Thermal design of satellites and spacecraft radiators.
Check heat dissipation from electronic components.
Physics coursework and homework problems on blackbody radiation.
Compare emissivity values for different surface coatings.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu