A novel, physically based kernel for population balance modeling of granule growth by coalescence is presented. This kernel is size-independent in that all collisions with an effective average granule size less than a critical value are successful. Simulations based on this kernel show that a variety of contradictory experimental observations can be modeled. In the limiting case of viscoelastic collisions, the kernel can be related to the governing group of the Stokes number (Ennis et al., 1991), representing the ratio of granule collisional kinetic energy to viscous dissipation brought about by the binder. In more general cases, material properties that control deformability, such as interparticle friction, binder viscosity, and liquid content, strongly affect this critical size. The kernel clearly demonstrates the three regimes of drum granulation originally proposed by Kapur and Fuerstenau in 1964 and compares favorably with the two-stage sequential kernel developed by Adetayo et al. in 1995 for the drum granulation of fertilizers.