A convenient adsorption kinetic equation based on film diffusion mass transfer and Langmuir equilibrium was developed. The model shows a straight line passing through the origin in a plot similar to the Boyd plot and the slope of the line is related to the film mass transfer coefficient. It can be used to analyze if an adsorption process is controlled by film diffusion and, if so, to determine the film mass transfer coefficient. The model was applied to four adsorption systems and compared with the Weber, the Boyd (or Reichenberg) and the Vermeulen (or Urano) models. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.