It is shown that the relative maximum void contraction and the corresponding relative fractional solid volume are only the functions of size-ratio for binary mixtures, which can be determined experimentally. A linear analytical model, directly based on the experimental results of binary mixtures, is developed. The results show that the calculated porosities for ternary mixtures are within 8% relative error of measurements. Good agreement between the theoretical and experimental results was also obtained for Gaussian and log-normal size distributions. It is concluded that the porosity of multi-component mixtures of particles may be confidently predicted from the results of binary mixtures.