Based on breathing-shell-model MD simulations with quantum correction, we calculated the temperature-pressure-volume (T-P-V) equation of state(EOS) of γ-Mg₂SiO₄ to be used as a reliable pressure calibration standard at temperatures up to 2000 K and pressures up to 25 - 30 GPa. The simulations use empirical interionic potentials, previously developed for the Mg₂SiO₄ system to reproduce accurately measured structural and elastic properties. The potentials are applicable not only to γ-Mg₂SiO₄, but also to α- and β-Mg₂SiO₄ over wide temperature and pressure ranges. We assessed the accuracy of the resulting T-P-V EOS of γ-Mg₂SiO₄, by using the recently reported data on simultaneous X-ray measurements of MgO and γ-Mg₂SiO₄, performed by using synchrotron radiation in a multi-anvil apparatus at high temperatures and pressures. We found that pressures estimated through the MgO EOS presented by Matsui et al. (2000) and those for the γ-Mg₂SiO₄ EOS agree very well, with the average differences in the estimated pressures between the two EOS’s less than 0.3 GPa at T between 1500 and 2000 K and P between 19 and 23 GPa.