Economically, the accuracy of flow rate computations under the gates of barrages is very important. Policy of water saving relies on the precision of the flow discharge measurements. This experimental study investigates the flow under radial gates with submerged flow conditions. A combination of dimensional analysis and the incomplete self similarity (ISS) concept was applied to propose a calibration equation for the submerged radial gates. The deduced equation relates the discharge to upstream and downstream water depths, gate opening, minimum jet thickness and water depth immediately downstream of the gate. Based on the experimental data, a reliable formula for the water depth immediately downstream from the submerged gate (water depth at vena contracta) was developed; this water depth is not cited in the literature for the submerged radial gates. This paper had also assessed the performance of several calibration formulas for submerged radial gates using the experimental data. The developed calibration formula was able to predict the submerged flow discharge with an accuracy of ± 4%. Three hundred and thirty two field-measured data sets were collected from Al-Tawfiki head regulator which sited at Delta Barrages district in Egypt to validate the proposed formula. Although, this regulator has more than one submerged radial gate operating in parallel, average associated errors of this equation are within ± 6%.