Point defects are known to be of paramount interest in materials because of their importance in diffusion processes, electrical conductivity, or mechanical properties during creep. Whereas vacancies in metals are frequently associated with a negative relaxation volume, in oxides, due to electrostatic repulsion, charged vacancies are expected to be characterized by a positive one. Because of this positive relaxation volume, the effect of high pressures on the vacancy formation remains a matter of debate. This study focuses thus on the relaxation volume of charged vacancies and interstitials in forsterite Mg2SiO4, and we also consider the case of MgO to investigate the effect of high pressure on the relaxation volume of charged vacancies. Performing first-principles calculations with the Quantum Espresso package, we aim at computing the relaxation volume of these point defects, as a function of their respective charge and under external pressure. Yet, due to periodic boundary conditions, the pressures obtained in DFT codes are ill-defined and need to be corrected to obtain relevant volume values. These corrections are based on the knowledge of the Absolute Deformation Potential (ADP), that we calculated using the strained superlattice technique. The relaxation volumes thus obtained enable us to discuss the weight of electrostatic interactions at high pressures on this property.