Stellar Luminosity Calculator
Enter a star's radius and surface temperature to calculate its luminosity in watts and as a multiple of the Sun's luminosity.
Use the Stellar Luminosity Calculator
Star Parameters
1 R☉ = 695,700 km
Sun ≈ 5,778 K | Blue supergiants up to ~50,000 K
Preset Stars
Enter star parameters and click Calculate
Results will show luminosity in watts, solar units, and absolute magnitude.
Luminosity Results
Solar Luminosities
—
L / L☉
Absolute Magnitude
—
M (bolometric)
Watts
—
Total power output
Stefan-Boltzmann Formula
L = 4π × R² × σ × T⁴
Comparison to the Sun
Summary
Stellar luminosity is the total energy a star radiates per second. This calculator applies the Stefan-Boltzmann law — L = 4πR²σT⁴ — to compute luminosity from a star's radius and effective surface temperature. Results are shown in watts and as a ratio to the Sun's luminosity (L☉ = 3.828 × 10²⁶ W), the standard unit used in astrophysics.
How it works
- Enter the star's radius in solar radii (R☉) or kilometers.
- Enter the star's surface temperature in Kelvin.
- The calculator applies the Stefan-Boltzmann law: L = 4πR²σT⁴.
- Results appear instantly in watts, solar luminosities, and absolute magnitude.
- Use the preset star buttons to explore well-known stars.
Use cases
- Astronomy students learning the Stefan-Boltzmann law.
- Compare the energy output of different stellar classes.
- Estimate a star's luminosity from observational data.
- Understand why giant stars vastly outshine dwarf stars.
- Explore how temperature dominates luminosity via the T⁴ relationship.
- Calculate luminosity for fictional stars in science fiction world-building.