Particle size distribution of the sample of waste sand from waste water treatment plant have been determined with two commonly used methods of mathematical models by Rosin-Rammler (RR model) and by Gates-Gaudin-Schuhmann (GGS model). On the basis of network analysis distribution function, F(d) (mass fraction) and density function, f(d) (number of particles captured between two screens) have been obtained. Experimental data have been evaluated using the RR model and GGS model, both models have been compared. Better results were achieved with GGS model, which leads to a more accurate separation of the different particle sizes in order to obtain a better industrial profit of the material.