Shape factors evaluate the efficiency of material usage in a structure. Previously, they have been developed for simple bending but, in practice, beams often have a more complicated bending response. Therefore, shape factors that account for asymmetric bending are introduced. The shape factors are applied to six example beam sections to demonstrate the effect of shape and load on structural efficiency. The shape factors are also enhanced for inclusion in a more general measure of structural efficiency, the performance index, comprising elements of both geometry and material. Next, a study is performed to show how the asymmetry of a beam section affects structural efficiency. The shape factors can quantitatively evaluate the structural efficiency of beam sections, demonstrating the effect of asymmetric bending on the structural response. Therefore, these shape factors can be used for concept selection and to provide insight into optimal structural design.