This study investigates optimal large-scale offshore wind turbines (OWT). The blade data for large-scale OWTs is developed using the NREL 5-MW baseline OWT and validated using the DTU 10-MW reference one, where the blade parameters for OWTs ranging from 5 to 17 MW are established. Interpolation, extrapolation, and regression analyses are used to obtain the relationship between the chord length and three blade properties, as well as the relationship between the nacelle mass and rotor diameter. The chord length and rotor radius are then adjusted based on the NREL 5-MW OWT to obtain the required rated power contour figure using FAST. One can use the rated power and critical blade out-of-plane deflection to determine the chord length and rotor radius factors, and the required FAST input files can thus be generated. In this study, 5- to 16-MW OWTs are selected to conduct a support structure analysis and to determine the optimal steel design. Based on the relationship between the rated power with the blade weight and the steel weight of the support structure, OWTs with a rated power ranging from 9 to 15 MW is suitable. The 12-MW one should be optimal, and those over 15 MW are not economic. (C) 2020 Elsevier Ltd. All rights reserved.