The angular degree (symbolized deg or °) is a unit of plane angular measure used in some engineering applications, and by most lay people. There are 360 angular degrees in a complete circle. Thus, one angular degree is equivalent to approximately 0.00277778 of a circle.
Opinions differ concerning the reason why 360 was chosen as the number of angular degrees to comprise a circle. One theory is based on the fact that 360 is approximately the number of days in a calendar year, is a reasonably round number, and can be divided into halves, quarters, and eighths and still obtain whole numbers. A half circle is 180°, 1/4 of a circle is 90°, and 1/8 of a circle is 45°. The Earth moves approximately 1° in its orbit around the sun every 24-hour day.
In mathematics, theoretical sciences, and formal engineering , the radian (rad) is preferred as the unit of plane angular measure. A radian, which is the unit of angular measure in the International System ( SI ), is equivalent to approximately 57.296°.
Also see the Table of Physical Units .