The assessment of orographic complexity is a central factor when determining the wind- and energy potential for proposed wind energy projects. Orographic complexity is particularly important for evaluating the suitability of flow models, as it can influence the limits of applicability of different models and methods. The criteria currently used in Technical Guideline 6, Revision 11 to assess orographic complexity is based on the method of IEC 61400-1, Ed.3, where complexity is characterized by the variations of the terrain topography from a plane, the radius of observation of which depends, among other things, on the hub height taken as a basis. However, it has been shown that this methodology does not meet the technical requirements for use in wind and yield potential assessments and, moreover, does not correspond to the subjective assessments of experts. In order to close these gaps, we present in this article a new pragmatical methodology for assessing terrain complexity, which was developed and validated within the framework of the FGW Expert Committee on Wind Potential (FGW FAWP). Additional aspects, such as variations in terrain, explicit design for wind and energy potential analysis, similarity between sites considered (e.g., location of wind measurement and location of proposed wind turbine), and consideration of terrain slope, were included. The application of this procedure allows an objective assessment of the terrain complexity and thus helps to define more precisely the limits of transferability of wind conditions using flow models.