Steel plate girders take advantage of transverse stiffeners giving web lateral support along the span and increasing the shear resistance. In addition, transverse stiffeners play a key role in mitigating web buckling by supporting the edges of the web panel and thus anchoring the axial compression resulting from the tension field action. For the design of transverse stiffeners, EN 1993-1-5 specifies the following requirements: (1) a strength verification, (2) a minimum elastic bending rigidity, and (3) a torsional rigidity check. However, prior studies have shown that the strength verification tends to be overly conservative, as it assumes internal forces significantly higher than those observed in experimental testing and numerical simulations. As a result, this requirement has been eliminated by design standards such as AASHTO and AISC, where stiffener design is governed solely by a verification of a minimum ultimate bending rigidity. This study draws upon the results of 13500 nonlinear elastoplastic finite element simulations to determine the necessary bending rigidity of intermediate transverse stiffeners to ensure the plastic shear resistance of the girder. A novel and simplified design method is proposed for intermediate transverse stiffeners in flat plate girders. This approach accounts for the influence of the flange, the web slenderness, the panel aspect ratio and material properties.