Angular Size Calculator

About this calculator

This calculator finds the angular size (apparent angular diameter) of an object as seen from a given distance: θ = 2·arctan(size / (2·distance)), or for small angles simply θ ≈ size/distance in radians. The result can be shown in degrees, arcminutes, or arcseconds.

Amateur and professional astronomers use it to predict how large the Moon, a planet, or a deep-sky object will appear in an eyepiece or camera sensor, while photographers and surveyors use it to work out framing and field of view at a given distance. Enter the object's actual size and its distance to get the apparent angle.