Clustering of granular gases is caused by the dissipation occurring in part
icle collisions. We use the generalized dimension, a measure for the inhomo
geneity of a spatial distribution of particles to characterize the structur
al evolution. Furthermore, we quantify the typical length scale of the clus
ters obtained by 3D simulations using the index of dispersion, a measure fo
r the deviation of the particle density from a Poissonian. We then derive a
n expression for the expected length scales of cluster formation from a sta
bility analysis in the hydrodynamical approximation. We find a good agreeme
nt between our theoretical prediction and numerical experiments.