Studies on the hydraulics of urban storm inlets have relied on dimensional analysis and numerical models to represent the capture process of the grates through empirical equations. The variety of formulations generates scattered knowledge that is difficult to compare due to the test hypotheses and the proposed applications. In order to increase the understanding of the catchment of urban grate inlets, the reanalysis of the experiments of three grates at full scale (1:1) is carried out, with total flows between 10 to 81 l/s, transversal slopes between 0.7 to 3% and longitudinal slopes between 2 to 8%. The traditional weir equation has been properly adjusted where the hydraulic head includes the flow velocity and depth head and the discharge coefficient varies between 0.05 and 0.232 depending on the Froude number of the approaching flow.