A free overfall at the end of an open channel provides a simple means for measuring flow discharge. The paper presents a simplified approach for the computation of end-depth of a free overfall in horizontal or mildly sloping inverted semicircular channels. Using a known end-depth the discharge can be estimated. The flow over a free overfall in an inverted semicircular channel is simulated by that over a sharp-crested weir to calculate the end-depth-ratio (EDR). The mathematical model is calibrated by the experimental data, making the coefficient of velocity a free parameter. The EDR, related to the critical depth, is around 0.705 for a critical depth-diameter ratio up to 0.42. The computed results agree satisfactorily with the experimental data. © 2001 Elsevier Science Ltd. All rights reserved.