A diffusion model is applied to calculate the turbulent mixing width at an ablating surface. It is proposed that the general model be tested first on well‐determined and easily accessible stabilizing mechanisms such as surface tension, viscosity, density gradient, or finite thickness. In this model the turbulent mixing widthhis directly correlated with the growth rate &ggr; of the perturbations in the presence of stabilizing mechanisms:h/hclass=(&ggr;/&ggr;class)1/2, wherehclass=0.07Ag&tgr;2and &ggr;class=&sqrt;Agk(whereAis the Atwood number,gis the acceleration, &tgr; is the time, andk=2&pgr;/&lgr; =2&pgr;/(&ohgr;hclass), &ohgr; being a dimensionless constant in the model). The method is illustrated with several examples forhablation, each based on a different &ggr;ablation. Direct numerical simulations are presented comparinghwith and without density gradients. In addition to mixing due to the Rayleigh–Taylor instability, the diffusion model is applied to the Kelvin–Helmholtz and the Richtmyer–Meshkov mixing layers. ©1996 American Institute of Physics.