Film thickness determines many key coating properties including gloss. However, current literature hardly addresses the development of methods to directly correlate film thickness with gloss. Thus, the lack of accurate models hinders further product design and optimisation of coating products and processes. In this contribution, a previously derived gloss-viscosity relationship is turned into a gloss-film thickness mathematical model. Experimental results of both matting and glossy agents are found to be successfully predicted by a model that is revealed as a simple and useful tool for day-to-day calculations.