The measure of an angle is determined by the amount of rotation from the initial side to the terminal side. One way to measure an angle is in terms of **degrees**. A measure of one degree (1°) is equivalent to a rotation of of a complete revolution.

To measure angles, it is convenient to mark degrees on the circumference of a circle. Thus, a complete revolution is 360°, half a revolution is 180°, a quarter of a revolution is 90° and so forth.