Answer
$\pi\text{ radians} = 180^\circ$; multiply degrees by $\frac{\pi}{180^\circ}$ to get radians.
Explanation
Common angles: $30^\circ = \frac{\pi}{6}$, $45^\circ = \frac{\pi}{4}$, $60^\circ = \frac{\pi}{3}$, $90^\circ = \frac{\pi}{2}$, $360^\circ = 2\pi$.