About this tool
The Magnitude & Distance Modulus Calculator is a free, in-browser astronomy tool that ties together a star's apparent magnitude (m), its absolute magnitude (M), and its distance through the distance-modulus relation m − M = 5·log₁₀(d) − 5, where d is the distance in parsecs. In distance-modulus mode you leave exactly one of the three boxes blank and the tool solves for it, also reporting the distance in light-years and the distance modulus μ = m − M.
A second brightness-ratio mode uses Pogson's scale: a difference of five magnitudes corresponds to exactly a factor of 100 in brightness, so the flux ratio between two stars is 100^(Δm/5) = 2.512^(Δm). Enter two magnitudes and the calculator reports how many times brighter the brighter star is, remembering that smaller magnitudes mean brighter objects.
All arithmetic runs locally in your browser with nothing sent to a server, so your inputs stay private. Magnitudes are dimensionless logarithmic quantities and distance is entered in parsecs (1 pc ≈ 3.26 light-years); the absolute magnitude is defined as the apparent magnitude an object would have at a standard distance of 10 parsecs.