An iterative refining method using FullProf software (Rietveld refinement) as a multi-input-output black-box with cyclic feedback is proposed in order to accurately measure the lattice misfit in two-phase coherent alloys. The method uses two X-ray diffraction spectra taken on the same powder sample. In addition, it requires the volumetric fraction of the phases and the size of the crystallite in the precipitated phase as derived from the measurements made by the transmission electron microscopy-energy dispersive spectroscopy technique. The measurement of the lattice misfit in a Fe2AlV-strengthened ferritic Fe76Al12V12 alloy is shown as an application of the method.