This paper reports the findings of a study of four particle packing models used to proportion the mix constituents (solid particles) of concrete to produce a minimum voids ratio (or maximum packing density). The models have been compared using laboratory tests and published data. The basic mathematics of the models is discussed, particularly how each model defines the particle size distribution of the solid particles. The models have been applied to both the aggregate (sand and gravel) and the cement phase (PC, PFA, GGBS and limestone fines) and the estimated voids ratio compared with that measured in the laboratory. It was found that the models give broadly the same output and suggest similar combinations of materials to give the minimum voids ratio. Using the materials considered it was found that the largest improvement in voids ratio was achieved with the aggregate phase. The particle sizes of the cements considered here were similar and, as a result, only small improvements in voids ratio could be achieved. It was noted that proportioning concrete mix constituents to minimise voids ratio did tend to produce a harsher mix than normal. However, using the mix suitability factor, proposed by Day (1999), reduced this problem. There are some detail differences between the models suggesting further refinements could be carried out and a modification to one of the models is provided.