A method is described for studying certain characteristics of the voids contained within a mass of aggregate particles. Measurements have been made on void cells dissected from single size aggregate systems of a variety of particle shapes in dense and loose packings. The measurements refer to the critical ratio of occupation and the critical ratio of entrance. From these measurements occupation size distribution curves and entrance size distribution curves can be drawn, analogous to particle size distribution curves. The application of the results to the problem of the design of aggregate gradings to minimum or controlled void content, by pre-mixing or filtration techniques, and of the related problem of segregation of mixed aggregates is discussed.