In order to design a steel member subjected to a bending moment and an axial load, there are an infinite number of possible solutions of I- or H???steel cross-sections, the doubly-symmetric solution being just one of them. This paper presents a procedure to obtain the optimal steel cross-section from the infinite number of possible solutions. The process is based on the Reinforcement Sizing Diagrams employed in reinforced concrete strength design. The procedure looks for any type of solution regarding compact or non-compact steel sections. All aspects related to local instabilities are taken into account, as well as some special considerations in order to address the global instabilities associated with the slenderness of the steel element