The allometric relationship between the height of barchan dunes and horn to horn widths is re-examined. The addition of new data from barchans in the Namib Desert and elsewhere confirms the relationship that the height of a barchan is approximately one-tenth of the width of the dune. Height and width of the dune are closely linked to the three-dimensional morphology of the dune, in particular, the relatively constant mean angles of around 11° at which the side slopes of the dune are maintained. We suggest that the 3-D barchan form is directly controlled by aerodynamic processes. Constant feedback between three-dimensional stoss face (windward) shape of the dune, slipface height and horn to horn width, and shear stress produces an equilibrium dune form. Keywords: barchans, dune height, horn width, morphometric relationships.