One has to understand the hydrostatic pressure when dealing with the Earth’s expansion. The hydrostatic pressure p in the center of the Earth can be calculated as follows:
The R-value is approximately 6378 km today, g– and ρ-values can be found for example in the PREM model.
We see that in order to compute the pressure, one must count all the products of acceleration due gravity and density towards the center of the Earth.
The today’s pressure in the center of Earth is approximately 360 GPa.