The equilibrium orbit theory and the residence time theory predict that the product between the Stokes number and the Euler number (Stk(50)Eu) should be constant for a family of geometrically similar hydrocyclones. It has been already shown that Stk(50)Eu is, in reality, a function of feed concentration and water flow ratio. For different families, this product is also a function of the cyclone geometrical proportions. In this work, data obtained with seven hydrocyclones was used to generate a model based on dimensionless groups capable to predict performance of hydrocyclones. Unlike other models that can be found in the literature, where the parameters have to be adjusted for each data set, the proposed model was able to reproduce data from the classical works of Rietema, Bradley and Kelsall. The assumption of invariance of the reduced grade efficiency curve adopted in this work seems to be a good approximation for performance prediction of hydrocyclones. The fish-hook effect could not be found in any of the 160 experiments, probably due to the apparatus used to determine size distributions, which measure a dynamically equivalent diameter known as Stokes diameter.