Abstract Decreasing the volume by applying pressure in many Cr alloy systems Cr 1− x A x produces a similar magnetic phase diagram to that obtained at ambient pressure by changing the concentration x of the dopant A. In several cases a decrease in electron concentration, in a rigid-band model, parallels a decrease in volume (and conversely). The experimental data are reviewed in terms of a universal magnetic phase diagram. It is proposed, in view of the failure of the canonical model of nesting electron and hole Fermi surfaces, which is commonly used to account for variation with composition of the magnetic properties of spin-density-wave Cr alloys, to explain the close parallelism between the effects of pressure and alloy composition, that their strong volume dependence has a quite different origin. The use of the magnetic anomalies around the ordering temperature in the thermal expansion and the bulk modulus is critically reviewed.