We use self-consistent field theory (SCFT) to study the interactions between a polymer-grafted spherical particle and a bare spherical particle and explore how these interaction energies depend on the radii of the two particles and the grafting density. We find that the magnitude of the interaction energies increases with the radii of both the grafted and bare particles and with increasing grafting density. We also find a universal scaling law for the interaction potential which exhibits a power-law dependence on both particle sizes, a linear dependence on grafting density, and a logarithmic dependence on interparticle distance with a range of interaction that scales with brush height. We compare our numerical results to those obtained using the Derjaguin approximation. (C) 2009 Wiley Periodicals, Inc J Polym Sci Part B Polym Phys 47 2566-2577, 2009