The present communication re-examines the basis of a previous model (E. S. Puchi-Cabrera: Surf. Coat. Technol., 2002, 160, 177 - 186) for the computation of the composite hardness of coated systems as a function of the relative indentation depth (RID), applicable to monolayer coatings. The results initially derived from simple geometrical considerations are compared with those obtained taking into account the volumes of the plastic zones of the coating and substrate under the indenter, as proposed by several models already published. A similar expression for the rate of change of the substrate volume fraction with the RID is obtained from both approaches. The consideration of the validity of a linear law of mixtures for the determination of the composite hardness is also reexamined, assuming that the composite hardness could be given by a harmonic law of mixtures. Both the previous model and the one developed from the introduction of a harmonic law of mixtures are extended to deal with multilayer coatings. In this case, the composite hardness as a function of the RID is calculated in terms of the volume fraction and hardness of each of the layer materials which compose the multilayer coating, and also two constants which characterise the behaviour of the coating. The results derived from the new model based on the harmonic law of mixtures are then compared with those obtained from the previous model, employing a number of systems involving both monolayer and multilayer coatings deposited onto different substrates.