A great deal of well-established and cutting-edge practices and reliable tools have been developed over the last decades to support hypersonic aircraft conceptual and preliminary design. Among these, the Hypersonic Convergence sizing approach for transonic to hypersonic vehicle applications first developed at formerly McDonnell Aircraft Company between 1970 and 1990, represents one of the most common in the field. An innovative approach to a such consolidated sizing methodology with relevant modifications is presented as main topic of this thesis. In particular, the integration of the Multiple Matching Chart Analysis tool, implemented in the last years by the Aerospace Engineering Department of Politecnico di Torino, to the classical procedure widely described in literature enables an important refinement of the design point searching algorithm, when the objective is to size SSTO (Single-Stage-To-Orbit) or TSTO (Two-Stage-To-Orbit) HTHL (Horizontal Take-off and Landing) vehicles.