Compaction of metal powders in a rigid die is an important step in the fabrication of parts by the conventional powder metallurgy (P/M) route. It is thus important to find out the relationship between the applied pressure exerted by the pressing tool and the densification of the compacted part (green compact). In this work, an expression based on the piston-equation approach is presented. The expression describes the relation between the applied pressure and the average relative density of the compact with considering two simultaneous mechanisms for powder compaction. These mechanisms are particle rearrangement and particle deformation. It is also possible to obtain the contribution of each mechanism in the material densification from the equation. Since porous materials contain only isolated closed pores at relative densities greater than about 0.95, it would be hard to have densification due to the rearrangement mechanism after achieving this value of relative density. This analysis is applied and verified for the die compaction of Fe, Cu and Ni powders. (C) 2015 Elsevier B.V. All rights reserved.