The effect of misfit strain on the equilibrium aspect ratio of isotropic islands has been investigated by using numerical calculations of the elastic strain energy of spherical caps on a substrate. The effects of three dimensionless quantities were investigated : the ratio of the surface energy to strain energy, the modulus mismatch and the ratio of the interfacial energy to the surface energy of the island. It was shown that values of these parameters that tended to increase the strain energy dominance resulted in larger equilibrium aspect ratios (height-to-width ratio). The effect of modulus mismatch was also studied. It has been shown that as the modulus of the substrate increases relative to the island (keeping all other parameters constant), the aspect ratio increases. Furthermore, it has also been shown that island-to-island interactions occur over very short ranges, becoming negligible when the midpoint of the islands are separated by more than two diameters.