Radian is a metric unit used to measure angles. Engineers and scientists frequently measure angles in radians because the unit simplifies many of their calculations. Navigators, surveyors, and most other people measure angles in degrees. One radian equals an angle of 57.29578 degrees.
An angle of 1 radian is formed between two radii of a circle if they mark off an arc equal to the length of the radius of the circle. Circles and arcs may represent angles and may be measured in radians. For example, the circumference of a circle equals 2 times pi times the radius of the circle. Thus, there are 2pi radians in a circle.
