The use of modular construction shows continuous growth leading to cost-effective and fast construction methods. Modular Construction Optimised (MCO) beams are employed in steel-framed modular units owing to their enhanced structural performance. MCO beams fall under the hollow flange beam family and can be produced using roll forming techniques, with lesser cost compared to general built-up beams. However, there is no dominant research on the design approach to predict the section moment capacity of MCO beams. To bridge this knowledge gap, this paper aims to investigate the section moment capacity of MCO beams using numerical analysis. Numerical models were developed as simply supported four-point bending arrangement in ABAQUS. The validity of the numerical models in terms of failure capacity prediction and failure modes were ensured comparing the experimental results of the hollow flange and lipped channel beams. Subsequently, a comprehensive parametric study was conducted including various dimensional and strength parameters to generate a section moment capacity results database. The results were compared with the codified Direct Strength Method (DSM) predictions and appropriate design recommendations were proposed. Based on the results, a simplified calculation method to predict the critical elastic buckling capacity of the MCO beams was also developed. New findings arising from this study would enhance the applicability of MCO beams in steel modular structures.