A square degree (deg2) is a non-SI unit measure of solid angle.
Other denotations include sq.
Just as degrees are used to measure parts of a circle, square degrees are used to measure parts of a sphere.
Analogous to one degree being equal to π/180 radians, a square degree is equal to (π/180)2 steradians (sr), or about 1/3283 sr or about 3.046×10−4 sr.
The whole sphere has a solid angle of 4πsr which is approximately 41253 deg2: