Most ceramic powders contain amounts of agglomerates. Hard agglomerates (aggregates) which do not break up during processing may retard compaction leading to a nonuniform pore-size distribution and/or the formation of internal cracks which act as strength-limiting flaws in the sintered product [1]. So far, however, there have been few reports on the quantitative estimation of aggregation. In this study, the aggregation number is correlated with the agglomeration parameter (A) by a simple model relating aggregate density to compact density. The experiments entailed determining the green densities of seeded pellets. Aggregate density was derived from the relation between the porosities and amounts of added seed. The models and experiments permit quantitative investigation of aggregation in ceramic powders.