Distance Modulus Calculator

About this calculator

This calculator finds a star's distance from its apparent and absolute magnitudes using the distance modulus: m − M = 5 · log10(d) − 5, where m is the apparent magnitude (how bright it looks from Earth), M is the absolute magnitude (its true brightness at a standard 10-parsec distance), and d is the distance in parsecs. Rearranging solves for d directly from the two magnitudes.

Astronomers use this whenever a star's true luminosity is known or estimated (for example, from its spectral type or from "standard candle" objects like Cepheid variables and Type Ia supernovae), letting them derive distances to objects far beyond the reach of parallax measurements. Enter the apparent and absolute magnitudes to get the distance.