A generalized viscosity equation of state including a single adjustable parameter for correlating and estimating the viscosity of ionic liquids at different temperatures and pressures is proposed. The similar shape and form of the curves (isotherms and saturation lines) observed in a density-pressuretemperature plot and in a viscosity-pressure-temperature plot (rho TP and mu TP plots), known as geometrical similitude, is the basis of the proposed model. Viscosity data available in the literature has been gathered, analyzed, and selected to finally construct a database of consistent data to obtain a general model. The generalized equation of state model includes a number of parameters that are determined by fitting the model using the selected experimental viscosity data of different types of ionic liquids. In total, 3857 viscosity data for 187 ionic liquids in the temperature range of 253-573 K and pressures from 1.0 up to 1500 bar have been considered. The generalized viscosity model has been compared with other existing approaches and results show that the new viscosity cubic equation of state model provides accurate and consistent results taking in account the simplicity of the generalized expressions, which contains only one adjustable parameter for each ionic liquid. (C) 2019 Elsevier B.V. All rights reserved.