This paper presents the functionality of a new software tool for the preliminary estimation of wing and tail weight, based on a quasi-analytical structural sizing method. The implemented method is based on the weight decomposition of each lifting surface into primary and secondary contributions. The primary weight of both wing and tail empennages is estimated by stationary sizing of the torque box structure, based on tension and compression stress analysis of stiffened panels for the lower and upper surfaces, and shear stress analysis for the spar webs. Aerodynamic loads are calculated by a vortex lattice method for various load cases, as specified by airworthiness regulations. Inertial reliefs on loads due to the mass of the lifting surface structure, fuel and engine are taken into account, as well as the weight penalties due to engine mounting, connections and aeroelastic effects at high speeds. The weight estimation of the secondary structure (fixed leading and trailing edges, flaps, etc.) is based on the use of empirical relations. Some coefficients have been defined to allow designers investigating the effect of new materials and manufacturing techniques on weight. The tool includes a parametric geometry model able to swiftly generate dedicated models both for the aerodynamic and structure solvers. As a result, proper aerodynamic load distributions can be generated very quickly for the structural analysis of any generic lifting surface. Hence, much more accurate results can be achieved than with any other existing class II weight estimation methods, yet with a computational time much shorter than using more sophisticated methods based on finite element analysis. The tool has been validated for a limited number of passenger aircraft including one regional twin turboprop, and a few medium and long range turbofan airplanes. The result of the weight prediction is outstanding, with an average error of 1% for both wing and tail components.