AbstractLaboratory experiments were conducted on a radial gate to evaluate the energy equation for free-flow calibration. The experiments were used to develop new equations for the radial gate contraction coefficient for free flow. These were compared to equations for the contraction coefficient of radial and vertical sluice gates developed from prior studies and potential flow theory. The new radial gate free-flow contraction coefficient was related to both the gate lip angle and the gate opening relative to the energy head on the gate. The pressure distribution and velocity distribution coefficients were also evaluated. The energy loss through the gate was expressed as a function of the velocity head in the vena contracta, with a gate energy loss coefficient that varies with the relative gate opening. With the revised energy equations, the free-flow discharge predictions were computed for three data sets: (1) experiments presented here conducted at the USWCL laboratory in 2004–2005, (2) experiments performed by Jan Tel in 2000 and earlier using the same USWCL facility operated over a narrower range of conditions, and (3) experiments performed in the early 1980s by Clark Buyalski in the Bureau of Reclamation’s hydraulics laboratory. The coefficients were developed based on the later USWCL data only. The average discharge computation error for the combined data sets was 0.37%, and the standard deviation was 1.03%. Submerged flow predictions are the subject of future work.