AbstractThe flexural buckling resistance of compressed columns is typically determined using the flexural buckling curves of EN1993‐1‐1. With advances in computing capabilities, it has become possible to obtain the flexural buckling resistance as a result of a geometrically and materially nonlinear analysis (GMNIA) using imperfections. In design practice, equivalent geometric imperfections are usually used, but their values are calibrated against GNIA analysis. In the present research work, welded box‐section columns are investigated and a proposal for relative slenderness and yield strength dependent equivalent geometric imperfection magnitudes is developed. The required equivalent bow imperfection magnitude is determined to achieve the same resistance level as the calculation according to Eurocode‐based buckling curves. GMNIA analysis are conducted on simply supported columns subjected to concentrated force. The steel grade varied between S235 and S960. Several different section geometries are studied, the relative slenderness ratio is varied between 0.3 and 2.2. Design curve is fitted to the results and recommendation is given for applicable equivalent geometric imperfection magnitudes for steel welded box‐section columns.