It is well established that ion bombardment of certain solids leads to the formation of a disordered, often amorphous, phase. Though it is not difficult to describe the fractional disordering (Fd) as a function of the depth and of the volume disordered per ion impact, there is still no adequate model which relatesFd, to the fraction of inert gas (FIB) that would be released during the thermal annealing or chemical dissolution of the disorder. It is shown that an analytically manageable relation betweenFdandFIBcan be obtained on the basis of four assumptions, the most critical of which is that each ion impact gives rise to a compact, rather than fragmented, disordered region. This relation is shown to be reasonably well obeyed with Al2O3, diamond, and ZrSiO4, making it possible to estimate both the effective depth of disordering (Rd) and the size of the disordered regions (Vd1/3).Rdfor 10-keV Kr bombardment is with all three substances roughly 140 A. Likewise,Vd1/3is 14–20 A with Al2O3, 13–16 A with diamond, 20–27 A with ZrSiO4, and thus similar to what is observed using alternative approaches (e.g. electron microscopy) with Al2O3, Ge, Si, and ZrSiO4.