An experimental study was made of the drum granulation process, using various sizes of glass spheres as the material which was granulated. It was found that when the amount of granulating liquid was less than that required to fill about 90% of the intragranular void space, the granule size was independent of time, drum speed, and drum loading. A model was developed which was able to relate the granule size, relative to the individual particle size, to the amount of granulating liquid. The granule size distribution depends on the distribution of liquid, which in turn depends on the manner in which the liquid and solid are mixed.