SummaryThe present study deals with introducing a novel approach toward estimating the effective width of flanged reinforced concrete shear walls (FRCSWs). Due to the paucity of studies in assessing the effective width of nonrectangular sections, this paper aims at proposing efficacious formulations for the effective width estimation of short, squat, and slender T‐ and U‐shaped reinforced concrete (RC) shear walls subjected to the simultaneous action of the axial and lateral loading. To this end, at first, FRCSWs are simulated in the flanged shear wall numerical laboratory (FlashLab) program, which utilizes the finite element Abaqus software to analyze the walls. Thereafter, employing the developed numerical models, an extensive parametric investigation is conducted for a wide range of the key parameters. General expressions have then been developed to estimate the effective width of flanged RC shear walls invoking the evolutionary polynomial regression (EPR) analysis in conjunction with the genetic algorithm (GA). To assess the capability of the established equations in predicting the effective width of flanged sections, R‐factors have been calculated for all the cases examined in this study, which ranged between 0.78 and 0.94. Furthermore, a comparison has been made among the results attained through the proposed methodology and those obtained using the conventional design codes. It was revealed that the relative error obtained employing the proposed formulations is less than that of the corresponding values of the design codes by approximately 30% on average. The superiority of the established framework stems from consideration of the following: (1) influential parameters, (2) effective width variations at different performance levels, (3) loading direction, and (4) type of the wall in the effective width calculation process.