The mechanical response of amorphous silica (or silica glass) under hydrostatic compression for very high pressures up to 25GPa is modelled via an elastic–plastic constitutive equation (continuum mechanics framework). The material parameters appearing in the theory have been estimated from the ex situ experimental data of Rouxel et al. Rouxel T, Ji H, Guin JP, Augereau F, Rufflé B. J Appl Phys 2010;107(9):094903. The model is shown to capture the major features of the pressure–volume response changes from the in situ experimental work of Sato and Funamori Sato T, Funamori N. Phys Rev Lett 2008;101:255502 and Wakabayashi et al. Wakabayashi D, Funamori N, Sato T, Taniguchi T. Phys Rev B 2011;84(14):144103. In particular, the saturation of densification, the increase in elasticity parameters (bulk, shear and Young’s moduli) and Poisson’s ratio are found to be key parameters of the model.