Radian

The radian (symbol rad) is the unit for measuring angles, and is the standard unit of angular measure used in many areas of mathematics.

The length of an arc of a unit circle is numerically equal to the measurement in radians of the angle that it subtends; one radian is just under 57.3 degrees.

An arc of a circle with the same length as the radius of that circle subtends an angle of 1 radian. The circumference subtends an angle of 2π radians.

A complete revolution is 2π radians (shown here with a circle of radius one and thus circumference 2π).

Conversions

Radians	Degrees
0	0°
π/12	15°
π/6	30°
π/4	45°
1	57.3°
π/3	60°
π/2	90°
π	180°
2π	360°

References

Wikipedia