The void fractions of loosely packed and tapped beds of particles of continuous size distributions are correlated by means of a proposed new semi-empirical relation. In this relation four parameters describing the following particle properties are included: (i) mean particle size, (ii) spread of the particle size distribution, (iii) particle density and (iv) particle shape. The adjustable constants in the relation were optimised using experimental void fractions and particle characteristics for a wide variety of powders mainly gathered from the published literature. The optimised relation correlated the loosely packed and tapped bed void fractions with correlation coefficients of 0.955 and 0.973, respectively, the correlation thus removing virtually all the scatter in the original data. A discussion is provided.