Abstract The operating behavior of a rotating detonation combustor is experimentally explored for stoichiometric H 2 –O 2 –N 2 mixtures for four combustor geometries to determine the role of cell width ( λ ) and combustor channel width ( w ch ) on the existence of detonation and number of waves. The ratio of nitrogen dilution ratio ( β = N 2 :O 2 ) of the oxidizer is varied from β = 3.76 (air) to β = 2, yielding a reduction in the cell width by a factor of two. The regime of successful detonation is bounded by a minimum normalized channel width of w ch / λ > 0.5, which agrees with the limit for classical detonation propagation in a rectangular channel. The number of detonation waves within the combustor ranges from n = 1–3, and increases in a predictable fashion when the normalized perimeter of a detonation front exceeds p / λ > 7.4. From the present work, it appears feasible to predict the existence and multiplicity of rotating detonations from the combustor geometry and mixture cell width.