The article is dedicated to the construction of the "bending moment – curvature" diagrams for rectangular cross-sections of reinforced concrete bending elements. Assumptions and equilibrium equations used in the construction of diagrams are given in the article. The algorithm for the construction of the "bending moment – curvature" diagram is shown. Diagrams constructed by the proposed algorithm are compared with experimental data and with the results obtained by the methods proposed by other authors. The equations for determination of key points of linearized "bending moment – curvature" diagrams for cross-section with different reinforcement ratio are proposed.