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Since bubbling fluidized-bed scaling laws were first developed, there has been some debate about their correct application and the relative importance of the various scaling parameters, in particular, the solid-to-gas density ratio. In this paper, we highlight the differences in the existing literature and present the results from experimental fluidized-bed systems where the solid-to-gas density ratio has been changed by varying degrees. From our results, we conclude that there is some flexibility for altering the solid-to-gas density ratio when scaling bubbling beds of Geldart group B materials up to particle Reynolds numbers of at least 12, but further work is needed to clarify the range of particle Reynolds numbers over which the density ratio requirement can be relaxed. In contrast, when scaling group A materials, we find that the density ratio is an important parameter even if the particle Reynolds number is small.