# How is wave refraction measured?

This allows you to calculate the refractive index $n$ of the material, which is defined as $n = \frac{\sin i}{\sin r}$, and generally has a value $1.003 < n < 2.43$.
From this you can find the speed of light in the material as $n = \frac{c \left(v a c u u m\right)}{c \left(m a t e r i a l\right)}$