The present paper aims to determine numerically in the Abaqus ^® software the parameters that have the greatest influence on the effective width of steel-concrete composite box girder bridges. In the technical standards and in the literature, there is no specific recommendation for calculating the effective width in steel-concrete composite box girder bridge. As an alternative, the existing recommendations for steel-concrete composite I-girders are adopted. Therefore, in the absence of standards recommendations for steel-concrete composite box girder bridges, there is a need for an investigation into the distribution of stresses at the steel-concrete interface, because if the effective width was admitted incorrectly, may result in costly or even unsafe solutions. For this purpose, the effective numerical width of 160 models of steel-concrete composite box girder bridges was determined, in which the study variables were the configuration of the transversal section, the slab height, the span length and the elements arrangement in the cross section. After analyzing the results, it was proposed a recommendation to determine effective width of steel-concrete composite box girder bridges.