The Murnaghan equation is derived, under certain assumptions, from the equations of continuum mechanics. It involves two adjustable parameters: the modulus of incompressibility K 0 and its first derivative with respect to the pressure, K ′ 0, both measured at ambient pressure. In general, these coefficients are determined by a regression on experimentally obtained values of volume V as a function of the pressure P. These experimental data can be obtained by X-ray diffraction or by shock tests. Regression can also be performed on the values of the energy as a function of the volume obtained from ab-initio and molecular dynamics calculations.