# Why is pi = 180 degrees radians?

Now think of half of it and focus on the crust or contour of it: What is its length? Well if an entire circle is $2 \pi \cdot r$ half will be only $\pi \cdot r$ but half a circle corresponds to 180° ok...Perfect....
Your arc length, for half circle, we saw that was $\pi \cdot r$ dividing by $r$...you get $\pi$ radians!!!!!!