# Radian

**Radian**, in geometry, metric unit for measuring angles, used to simplify calculations. The radian measure of an angle is the ratio *a/r; a* being the length of the arc intercepted by the given angle; and *r* being the radius of the circle. An angle of approx. 57.3 (or 360° divided by 2 pi) = 1 radian.

*See also:* Angles.

## Additional topics

21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Providence to Rafflesia