It is postulated that the effect of absolute particle size on particle packing be modelled by use of (i) an initial porosity to take into account the packing of mono-sized particles and (ii) the concept of packing size ratio as a measure of the particle-particle interaction in forming a packing of mixed powders. This hypothesis is tested by the experimental measurements of the standard poured and tapped packing densities of white fused alumina powders. The results indicate that simple measurements can lead to the formulation of equations to quantify initial porosity and the packing size ratio. The porosity of multicomponent mixtures of powders can be predicted by the modified linear packing model as facilitated by the equations formulated.