Counting the number of contact points on a particle in a packed bed is a time-consuming processes. So, usually, the number of contact points on a particle surface in a randomly packed bed, i.e, tho coordination number, is estimated from the void fraction. Many researchers have proposed equations to estimate the coordination number From the void fraction in a packed bed, but all of these equations are obtained for a uniform sized sphere bed, Most actual powder has a wide size distribution, and the effect of the size distribution on the relation between the coordination number and the void fraction is very important. We investigated the effect of the size distribution on the relation using our model and a computer simulation, Based on our results, the coordination number is not changed with the size distribution of the particle bed: however, the void fraction becomes smaller for wider particle size distributions. It means that the value of the coordination number, as estimated by conventional equation for equal spheres from void fraction data, is overestimated for a randomly packed bed of multi-component spheres with wider particle size distributions.