The ultimate load capacities of conical and pyramidal shell foundations on unreinforced and reinforced sand were determined by laboratory model tests and numerical analysis. The results were compared with those for circular and square flat foundations. Eight foundation models on unreinforced and reinforced sand were tested in which the influence of shell configuration on ultimate load capacity was investigated. Both the experimental and numerical studies indicated that, if shell foundation thickness increases, the behavior of the shell foundation on either reinforced sand or unreinforced sand gets closer to that of flat foundations. A new factor was also defined to present a unique relation between the ultimate load capacity of shell and flat foundations.