The Earth doesn't have a single "radial thickness" like a sphere. It's made up of layers with different thicknesses:

* Crust: Varies from 5 km (oceanic crust) to 70 km (continental crust)

* Mantle: About 2900 km thick

* Outer Core: About 2200 km thick

* Inner Core: About 1220 km thick

So, the total radial distance from the Earth's surface to its center is about 6371 km.