Particle packing models have been studied extensively during past decades and led to development of some complex and relatively accurate predictions of packing of granular materials. While the models are capable of calculating the packing density for different volumetric share of constitutes, the concept of optimum packing remains unclear. The study aims to define optimum packing based on particle packing theory and excess water layer theory. The approach makes it also possible to calculate amount of paste that is required to put a concrete mixture at the onset of flow. Some pilot tests conducted in the laboratory showed good agreement with calculated data.