In the past few years, in-operation modal analysis has become a valid alternative for structures where classic forced vibration tests would be difficult, if not impossible, to conduct. A disadvantage of this method is that the excitation forces are unknown. Therefore, not all modal parameters can still be estimated. As a result, operational mode shape estimates remain unscaled (dependent on the unknown level of excitation) what restricts the applicability of operational modal models. So far, no techniques are available for the correct re-scaling of operational mode shapes purely based on experimental output-only data. All known methods involve either a detailed knowledge of the material characteristics of the test structure (finite element model approach) or make very restrictive assumptions about the excitation signal. In this contribution, a sensitivity-based method is proposed for the scaling of operational mode shapes on a basis of operational modal models only.