The Theoretical Spread Rate or coverage of a coating is a function of the coating's solids content. This value is useful in comparing coatings systems. In actual applications, there are losses. The practical spreading rate accounts for these losses. Losses result from application technique, losses to wind and environment, application equipment, and type of the substrate to be coated and substrate surface profile.
Wet Film Thickness = Spread Rate for 100% solids coatings.