⭐Stellar Magnitude Calculator
Convert between apparent magnitude, absolute magnitude, and distance. Remember: on this scale, lower (even negative) numbers mean brighter, not dimmer.
Compare two magnitudes to see how many times brighter one star is than the other, using the Pogson ratio.
Free Stellar Magnitude Calculator
Trying to work out how bright a star really is, not just how bright it looks from Earth? Our free Stellar Magnitude Calculator converts between apparent magnitude, absolute magnitude, and distance using the standard formula M = m − 5log₁₀(d) + 5. Enter any two values and the calculator solves for the third — with a toggle between parsecs and light-years for distance.
A built-in brightness-ratio tool also lets you compare two magnitudes directly, showing exactly how many times brighter one star is than another using the Pogson ratio — because on the magnitude scale, lower (even negative) numbers mean brighter, not dimmer.
Try the built-in presets for the Sun, Sirius, Betelgeuse, and Polaris to see real examples. No sign-up, no downloads, no limits. See the About page or the FAQ for more.
About the Stellar Magnitude Calculator
Features
Solve for m, M, or distance
Enter any two values and the calculator finds the third, with the substituted formula shown.
Parsec / light-year toggle
Enter or read distance in whichever unit you prefer.
Brightness-ratio tool
Compare two magnitudes directly using the Pogson relation to see exactly how many times brighter one star is.
Real star presets
Load the Sun, Sirius, Betelgeuse, or Polaris to see the formula applied to known values.
Frequently Asked Questions
What is absolute magnitude?
A star's brightness as it would appear from a standard distance of 10 parsecs, allowing fair comparison between stars.
What is apparent magnitude?
How bright a star appears from Earth, which depends on both its true brightness and its distance.
How does this calculator work?
Enter any two of apparent magnitude, absolute magnitude, and distance, and it solves for the third using M = m − 5log₁₀(d) + 5.
Is it free?
Completely free, no sign-up, downloads, or limits.
Why is a lower magnitude brighter?
The magnitude scale is inverted and logarithmic — a historical convention — so smaller (even negative) numbers mean brighter objects.
Can I compare brightness between two stars?
Yes, use the brightness-ratio section: enter two magnitudes and see exactly how many times brighter one is.
Can I use light-years instead of parsecs?
Yes, there's a unit toggle for distance between parsecs and light-years.
What happens if I enter a distance of zero?
The calculator rejects it, since the logarithm is undefined at zero.
Is my data stored?
No; everything runs in your browser and isn't stored or sent anywhere.
Does it work on mobile?
Yes, fully responsive on all screen sizes.