# Radian The radian (rad) is a unit for measuring angles. It represents the length of an angle's arc, in terms of the radius of the arc. An angle of $2 \pi \: \text {rad}$ is thus a full [[circle]], and $\pi \: \text {rad}$ half a circle. ## Converting To/From Degrees $\degree \rightarrow \text{rad:} \quad x \degree = \frac{x}{180} \pi \text \: {rad}$ $\text{rad} \rightarrow \degree \text : \quad x \: \text {rad} = \frac{x}{\pi} \cdot 180 \degree$