The Zener model for elastic sphere impacts has been solved with high accuracy and was used to evaluate the inelasticity parameter as well as the coefficient of restitution (CoR) for different material combinations and size ratios. Additionally, the model was modified to find a comfortable solution for the CoR. The proposed approach approximates the Zener model well for larger CoRs. Both models have been used to evaluate the CoR of gamma-Al2O3 and zeolite-4A granules and elastic-plastic spherical particle products at impact with glass plates of different thicknesses.