Packing density has great effect on the performance of a concrete mix. However, little research has been carried out on the packing density of cementitious materials owing to the lack of an established measurement method. Herein, a new method, called the wet packing method, is presented. With this method, the packing densities of blended cementitious materials, consisting of ordinary Portland cement (OPC), pulverised fuel ash (PFA) and condensed silica fume (CSF), were measured. The results verified the theory that the packing density could be significantly increased by blending two or even three cementitious materials together. Comparison between the measured results and the predicted values by three existing packing models, together with some additional tests, revealed that in the presence of a third-generation superplasticiser, the packing density of CSF is dependent on the lime content. When the lime-containing OPC and PFA contents are low, the CSF particles would flocculate and pack rather loosely, but at higher OPC and PFA contents, or with lime added, the CSF would pack to a higher density. With the effect of lime accounted for, very good agreement between the measured results and the predictions by the packing models was achieved.