Kerb-opening inlets have been used extensively in urban and highway drainage systems. Until quite recently the numerical solution of equations for determining the water surface profile and kerb-opening inlet discharge was tedious, with the result that approximate methods were used, based on experiments conducted over a limited range of the many variables involved. In this study a new hydraulic design procedure for kerb-opening inlets is developed from theoretical and experimental data. Since there was little difficulty in balancing the momentum equation using observed values of flow depths, velocities and kerb-opening inlet discharges, the possibility of using the momentum equation in a computer solution to replace the traditional energy equation was very attractive. The results are presented in diagrammatic form for practical use. The interception ratio of kerb-opening inlets to main street discharge can be presented by dimensionless parameters related to length of kerb-opening inlets, Froude number at the beginning of the kerb-opening inlets and width of spread on the main street. Experiments generally cover supercritical regimes and observed water surface profiles. Derived expressions for the length and interception capacity of kerb-opening inlets are compared with experimental results.