Electrozone sensing is a rapid and effective method that has been widely used for particle size analysis. This method is based on the Coulter principle, which provides a measure of the solid volume of particles. However, for wastewater particles, due to the high porosity of these particles, the measured Coulter size is significantly less than the physical dimension of these particles. To quantify this effect, the size distribution curves of the sieved wastewater particles were measured using the Coulter particle sizing method, microscopy technique, and sieving methods. A theoretical model was developed by accounting for the porosity of wastewater particles to correlate the physical size of these particles to Coulter size measurement. However, this theoretical model underestimated the size of wastewater particles smaller than 100m. Instead, the wastewater particles size (D) for both primary and activated sludge samples was found to be linearly related to the Coulter particle size measurement (d) according to: D=2.14d with r2=0.98.