Star Magnitude Calculator

Calculate absolute magnitude from apparent magnitude and distance using the distance modulus formula. Includes luminosity ratio and parallax.

Inputs

Apparent Magnitude (m)

Distance

Tab to move between fields

Results

Absolute Magnitude (M)

Distance Modulus

0 mag

Luminosity (vs Sun)

34.04 L☉

Distance32.62 ly

Distance2,062,650 AU

Flux Ratio (vs 10 pc)1

Brightness (vs Vega)0.3981

Parallax0.1 arcsec

How to Use This Calculator

Enter the star's Apparent Magnitude (m) as observed from Earth — Sirius is −1.46, the Sun is −26.74, and the naked-eye limit is about +6.
Enter the Distance (pc) to the star in parsecs — 1 pc = 3.26 light-years; Proxima Centauri is 1.3 pc.
Read Absolute Magnitude (M) — the star's intrinsic brightness at a standard 10 pc distance.
Use Luminosity (vs Sun) to compare output with familiar stars — the Sun is 1 L☉, Rigel is ~120,000 L☉.
Check Parallax (arcsec): stars within ~100 pc have measurable parallax with Gaia-class precision.

How the result changes with Distance

Distance	Absolute Magnitude (M)	Distance Modulus	Luminosity (vs Sun)
100,000	-19	20 mag	3,404,081,897.01 L☉
350,000	-21.72	22.72 mag	41,700,003,238.37 L☉
650,000	-23.06	24.06 mag	143,822,460,148.67 L☉
900,000	-23.77	24.77 mag	275,730,633,657.81 L☉

What each input means

Apparent Magnitude (m): Observed brightness as seen from Earth (Sirius = -1.46, Sun = -26.74, faintest naked eye ~ +6)
Distance: Distance to the star in parsecs (1 parsec = 3.26 light-years = 206,265 AU)

How this is calculated

Formula

M = m - 5 × log₁₀(d/10)

Worked example, using the default values

Identify Input Parameters
Apparent Magnitude (m) = 1, Distance = 10 = 2 input(s) provided
Calculate Absolute Magnitude
Absolute Magnitude
1 = 1
Calculate Distance Modulus
Distance Modulus
0 = 0
Calculate Luminosity
Luminosity
34.04 = 34.04
Calculate Distance
Distance
32.62 = 32.62
Calculate Distance
Distance
2062650 = 2062650

Engine last updated August 5, 2026. Checked against 2 independently-derived tests — how we verify calculators.

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