In fcc/bcc phase transformation systems, the orientation relationships (ORs) are usually described by parallelism of a set of specific vectors pairs or small deviations from the parallelism. This method often reflects the characteristic feature of the phase transformation correspondence. With the application of the electron backscatter diffraction (EBSD) technique to the measurement of the ORs, the ORs are also evaluated by a rotation matrix or a group of Euler angles. However, this quantitative description does not provide an intrinsic relationship between the crystallography equivalent variants. Thus, self–consistency of the data from different variants with an identical OR is not reflected directly by the data. In this paper, formulas have been derived to convert the OR identified by the relative orientation of a specific st of vectors to the OR described by Euler angles in data from EBSD. This method is useful fr acquiring self–consistent OR of small number of variants. Compared with the fitting method using high–indexed pole figures, which requires existence of many variants, the present method has broader applicability. An application example is given to deermine the OR between two pases in a duplex stainless steel from the measurement data of two variants. A slight deviation from an exact twin relationship between the variants has been characterized.