The paper presents an analytical methodology and a computational algorithm for evaluating the deformation parameters and crack width in reinforced concrete members subjected to eccentric compression combined with torsion. The members are fabricated from lightweight high-strength concrete. The proposed approach is based on the equilibrium equations for a spatial cross-section, the hypothesis of a spatial cracking surface, and the incorporation of the strain effect along the crack faces intersected by a reinforcing bar. A comparative analysis is carried out between the analytical predictions and experimental data on the deformation behavior and crack opening characteristics of the structural members under consideration. The experimental program was conducted on specimens made of lightweight concrete of strength classes B40 and B65, with rectangular cross-sections of 100×50 mm. It was found that the failure mode of the members is brittle, governed by the propagation of a single spatial crack developing progressively under loading. A comparison of the calculated crack widths obtained using the proposed methodology with the experimental results demonstrates satisfactory agreement, thereby validating the reliability of the analytical model. The findings highlight the necessity of accounting for the discrete nature of crack formation and the strain effect when assessing crack widths in lightweight high-strength concrete structures.