180° = π radians = 200 gradians = 0.5 turn. 1 radian = 57.2958°. 1° = 60 arcminutes = 3,600 arcseconds = 0.017453 rad.
Example: 90° is 1.5708 rad (π/2), 100 gradians, or a quarter turn.
Multiply degrees by π/180 (about 0.017453). For example 45° × 0.017453 = 0.7854 rad.
Multiply radians by 180/π (about 57.2958). One radian is roughly 57.3°.
See also: length converter · frequency converter · aspect ratio calculator