The stability behavior of steel structures is important when performing design. Standards (such as EN 1993-1-1 – Eurocode 3 Part 1-1) take the stability of steel members into account and allow for verifications using reduction factors or by sec-ond order theory analysis considering equivalent geometric imperfections. Eurocode 3 is well-suited for I-sections as the reduction factors and equivalent geometric imperfections have been calibrated using experimental and numerical data for this profile type. However, when it comes to U-sections, the standard lacks clear speci-fications. In literature, some authors have studied the stability behavior of U-sec-tions. For example, the imperfections required for performing a detailed geometri-cally and materially nonlinear analysis with imperfections included (GMNIA) as well as the residual stresses for U-sections have been studied. Nevertheless, there are still gaps to be addressed such as the equivalent geometric imperfections for second order theory analysis. In this paper, the lateral torsional buckling capacity of U-sections is determined by GMNIA, and subsequently corresponding equivalent geo¬metric imperfections for second order theory analysis are calibrated and proposed.