Angular Size Calculator
Find an object's angular size in the sky from its true size and distance, or solve for either, with this free astronomy calculator in your browser.
100% FreeRuns in your browserBasic
Enter Values
Minimum 0
Minimum 0
Enter your values and press Calculate to see results.
How to use this calculator
- Enter the object's size and its distance (same unit).
- Read the angular size.
How it works
Angular size = 2 × arctan(size ÷ (2 × distance)).
Worked example
Moon: 3474 km at 384,400 km. ≈ 0.52°.
Common mistakes
- Using different units for size and distance.
- Forgetting it's the full diameter, not the radius.
Frequently asked questions
Why do the Sun and Moon look the same size?
Coincidence of geometry — both span about half a degree, which is why total solar eclipses work.
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Explore more in Astronomy & Navigation.
Cite this tool
Zerdly. (2026). Angular Size Calculator. Retrieved from https://www.zerdly.com/tools/angular-size-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.