For the stability assessment of members and structures according to EN 1993-1-1, the equivalent member method, the geometrical non-linear calculation with equivalent geometrical imperfections or the GMNIA analysis with geometrical imperfections and residual stresses can be used alternatively. The second possibility requires a corresponding model for the cross-section resistance. For the verification of lateral torsional buckling, bow imperfections e₀ out-of-plane are defined, which lead in combination with the given loading in-plane and the geometrical non-linear analysis to bending moments M_z and torsion of the members. The amplitudes of the imperfections are highly dependent on the nature of the approach (e.g., scaling of the buckling shape, assumption of bow imperfections) and the verification method for the members. Within the framework of the scientific work supervised by the TU Dresden and TU Darmstadt, extensive parametric studies were conducted to calibrate imperfections for lateral torsional buckling based on the GMNIA. After determining the nature of imperfections and the design models for section resistance, this article presents results of these parametric studies and shows the calibration of imperfections for a standardisation proposal based on EN1993-1-1. The evaluation of the data in combination with the necessary simplifications for the design practice leads to appropriate definitions of imperfection values e_0,LT and the necessary differentiations.