However, it's important to note:
* This is an average. The thickness varies significantly depending on the location. Mountain ranges have thicker crust than plains, for example.
* The measurement is complex. The crust isn't a uniform layer. It has a denser lower layer called the "lower crust" and a thinner upper layer called the "upper crust."
* Oceanic crust is thinner. Oceanic crust is much thinner than continental crust, averaging about 4 miles (6 kilometers) thick.
So, while 20-30 miles is a good general estimate, it's helpful to remember that the thickness of the continental crust can vary greatly.
