About the Angular Diameter Calculator
Calculate an object's angular diameter, true size, or distance using ฮด = 2ยทarctan(d/2D).
What it is
The Angular Diameter Calculator relates an object's true physical size, its distance, and how large it appears from Earth. Enter any two of true diameter, distance, and angular diameter, and it solves for the third using the exact arctan formula โ the same relationship that explains why the Moon and the Sun appear almost the same size in our sky despite one being 400 times larger and 400 times farther away.
Features
Solve for any variable
Enter any two of diameter, distance, and angular size to find the third.
Unit flexibility
Diameter and distance in km, miles, AU, or light-years.
Presets
The Moon, the Sun, Jupiter, and a distant-star example with real values.
Auto-scaling units
Results shown in degrees, arcminutes, or arcseconds depending on scale.