What stellar luminosity is
Luminosity is the total energy a star radiates per second. This calculator estimates a star’s luminosity relative to the Sun using its radius and surface temperature.
The formula
Based on the Stefan-Boltzmann law, luminosity scales as L = 4πR²σT⁴. Expressed relative to the Sun, this simplifies to L/L☉ = (R/R☉)² × (T/T☉)⁴, using the Sun’s surface temperature of about 5,778 K as the reference.
This is the standard astrophysical formula for a star approximated as a blackbody radiator; it is intended for general educational and reference use.
Last reviewed August 2026