Magnitude Brightness Ratio Calculator

About this calculator

Astronomical magnitude is a logarithmic brightness scale where lower (or more negative) numbers mean brighter objects, and each step of 5 magnitudes corresponds to exactly a 100× difference in brightness. Pogson's law formalizes this: the brightness ratio between two objects is I₁/I₂ = 100^((m₂−m₁)/5) = 2.512^(m₂−m₁), where 2.512 (the fifth root of 100) is often called the "Pogson ratio" — the brightness multiple for each single magnitude step.

Astronomers, both professional and amateur, use this conversion to translate catalog magnitude differences into an intuitive "how many times brighter" figure — for example, the Sun (magnitude −26.7) is about 400,000 times brighter than the full Moon (magnitude −12.7) as seen from Earth. It's a standard step when comparing stars, exoplanet transit depths, or telescope limiting magnitudes.