Star Magnitude Brightness Ratio Calculator
Fill in the values and the answer updates as you type.
How the Star Magnitude Brightness Ratio Calculator works
The magnitude scale is logarithmic and runs backward: a smaller number is brighter. A difference of 5 magnitudes is exactly 100 times in brightness, so one magnitude is a factor of about 2.512. Brightness ratio = 100^((mB − mA) ÷ 5). A value below 1 means star A is fainter than star B. Example: with Apparent magnitude of star A 0.5 mag and Apparent magnitude of star B 4.5 mag, the result is Star A brightness compared with star B (times) = 39.81; Magnitude difference = 4; Brighter star = Star A.
Inputs and results
The Star Magnitude Brightness Ratio Calculator takes 2 inputs and gives 3 results.
What you enter
- Apparent magnitude of star A (mag) — starts at 0.5.
- Apparent magnitude of star B (mag) — starts at 4.5.
What you get
- Star A brightness compared with star B (times)
- Magnitude difference
- Brighter star
Example: Star Magnitude Brightness Ratio Calculator with the starting values
With apparent magnitude of star a 0.5 mag and apparent magnitude of star b 4.5 mag, the calculator returns:
| Star A brightness compared with star B (times) | 39.81 |
|---|---|
| Magnitude difference | 4 |
| Brighter star | Star A |
Change any value above and the results update straight away.
Star Magnitude Brightness Ratio Calculator FAQ
How do I use the Star Magnitude Brightness Ratio Calculator?
Enter apparent magnitude of star a and apparent magnitude of star b in the fields, then read star a brightness compared with star b (times), magnitude difference and brighter star in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Star Magnitude Brightness Ratio Calculator calculate?
How many times brighter one star is than another from their magnitudes. It returns star a brightness compared with star b (times), magnitude difference and brighter star from the 2 values you provide.
What values does the Star Magnitude Brightness Ratio Calculator start with?
It opens with apparent magnitude of star a 0.5 mag and apparent magnitude of star b 4.5 mag so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Star Magnitude Brightness Ratio Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Star Magnitude Brightness Ratio Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.