Scanning tunneling microscopy images of 4.5° misoriented double B stepped Si(001) have been analyzed to determine the double-layer step-edge formation energies of the energetically stable double step (B-type) as well as the energetically unstable double step (A-type). The ordering of the various single- and double-layer step-edge formation energies is in accordance with semiempirical tight-binding-based total-energy calculations performed by Chadi [Phys. Rev. Lett. 59, 1691 (1987)]. Finally, the miscut angle at which the transition between the single- and double-layer stepped surface occurs as calculated using the experimentally obtained step-edge formation energies is in agreement with the experiments.