Thin polymer coatings produced from water- and organic-solvent-based precursor liquids are ubiquitous components of industrial and consumer products. Design and optimization of dryers for these coatings require accurate predictions of their drying rates. Accurate drying predictions for many polymer/solvent coatings require a satisfactory description of the polymer/solvent mutual diffusion coefficients. A method is proposed to determine a satisfactory description of the diffusion coefficients by effective free-volume theory parameters. The effective parameters are determined from gravimetric data measured in a bench-scale drying apparatus. The application of the method to a poly(vinyl acetate)/toluene solution shows that the effective free-volume parameters give diffusion coefficients that agree with published data. The method is also applied to a rubber-based adhesive in industrial-grade heptane by treating the complex adhesive as a pseudobinary solution. For both systems the effective parameters lead to quantitatively accurate drying predictions in a pilot-scale oven.