Absolute & Apparent Magnitude Calculator
Enter any two of apparent magnitude, absolute magnitude, or distance and this calculator solves for the third using the distance-modulus relation.
mag
mag
pc
- 1
log₁₀(d / 10)
log₁₀(100 ÷ 10) = 1 - 2
Distance modulus
5 × 1 = 5 - 3
Absolute magnitude
5 − 5 = 0
How does this calculator work?
Absolute magnitude M relates to apparent magnitude m and distance d (parsecs) by M = m − 5·log10(d/10). Enter any two of m, M, and d, and the calculator solves for the third, also reporting the distance modulus m − M and the distance in light-years assuming no extinction.
Formula
How this is calculated
Apparent magnitude m measures how bright a star looks from Earth, while absolute magnitude M is how bright it would appear if placed at a standard distance of 10 parsecs. The quantity m − M is called the distance modulus and depends only on distance d (in parsecs).
The governing relation is M = m − 5·log10(d/10), which rearranges to m − M = 5·log10(d) − 5. Given any two inputs, the third follows: solve for M directly, solve for m by adding the modulus, or solve for distance with d = 10^((m − M + 5)/5). Distance is also reported in light-years using 1 pc ≈ 3.26156 ly.
The model assumes no interstellar extinction (no dimming by dust) and uses the magnitude system where smaller numbers mean brighter objects. Distance must be positive; values are undefined for d ≤ 0, so leave distance blank and supply both magnitudes if you want to find it instead.
Frequently asked questions
Apparent magnitude is how bright a star appears from Earth; absolute magnitude is how bright it would appear from a fixed distance of 10 parsecs, allowing fair comparison of true luminosities.
Leave the distance field blank and enter both magnitudes. The calculator uses d = 10^((m − M + 5)/5) parsecs, the distance-modulus formula.
The scale is historical and logarithmic: a difference of 5 magnitudes equals a factor of 100 in brightness, and lower (even negative) numbers correspond to brighter objects.
Also known as
TG we-Calculate Editorial Team. (2026). Absolute & Apparent Magnitude Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/absolute-magnitude-calculator
TG we-Calculate Editorial Team. "Absolute & Apparent Magnitude Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/absolute-magnitude-calculator.
TG we-Calculate Editorial Team, "Absolute & Apparent Magnitude Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/absolute-magnitude-calculator
@misc{wecalculate_absolute_magnitude_calculator, title = {Absolute & Apparent Magnitude Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/absolute-magnitude-calculator}}, year = {2026}, note = {TG we-Calculate} }
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