**Radian Circle Chart**. Firstly, one radian = 180/pi degrees and one degree = pi/180 radians. This site uses the circle constant τ (tau) instead of π (pi) when measuring angles in radians.

Therefore, for converting a specific number of degrees in radians, multiply the number of degrees by pi/180 (for example, 90 degrees = 90 x pi/180 radians = pi/2). A unit circle chart involves a circle with two lines dividing it into quarters. For a given angle θ each ratio stays the same.