Refraction is caused by the change in speed experienced by a wave when it changes medium. Dividing speed by frequency gives you the wavelength. For example the speed of light through water is 22500000 kms.
If you want to calculate the wavelength of a wave then all you have to do is plug the waves speed and waves frequency into the equation.
Finally calculate the index of refraction. If you want to calculate the wavelength of a wave then all you have to do is plug the waves speed and waves frequency into the equation. The index of refraction of some common materials are given below. A medium with a higher refractive index is an optically denser medium.