The radiative collapse of a Z pinch in hydrogen or helium is examined from a practical viewpoint. The maximum density that may be achieved is calculated by modifying the Pease–Braginskii current to include the effect of opacity and by incorporating the pinch into a realistic circuit. It is found that the maximum density is increased by the addition of series inductance inside the vacuum chamber. In most cases the density limit is determined by the pinch becoming optically thick, although for low line density and large series inductance the limit may be set by the onset of electron degeneracy. Pinches in hydrogen lead to denser collapsed states than pinches in helium.