How to use the angular size calculator
Find the angular size of an object at a distance. Enter object diameter, distance in the fields above; the angular size are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “how big does the moon look”, “apparent size”, “small angle”, “calculate angular size”, “find angular size”.
Formula
Variables
- D — Object diameter (km)
- d — Distance (km)
Worked example
With object diameter = 3474 km, distance = 384400 km, the calculator gives angular size ≈ 0.5178048 °; angular size ≈ 31.06829 arcmin.
Frequently asked questions
What is the angular size calculator used for?
Find the angular size of an object at a distance. It helps with questions such as “how big does the moon look”, “apparent size”, “small angle”.
What is the formula for the angular size calculation?
Angular size (°) = 2 × atan(D / (2 × d)). Angular size (arcmin) = [Angular size] × 60. Here D is object diameter (km), d is distance (km).
What inputs do I need for the angular size calculator?
You need object diameter in km, distance in km. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the angular size calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the angular size result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.