A relation for rapidly predicting the peak outflow rate from a breached embankment dam has been presented. The prediction equation is based on reliable data from 19 embankment dam failures and requires as input the volume of water in the reservoir at the time a breach begins to form, and the estimated height of the final breach. Peak outflow predicted by the equation can be used with simplified flood routing procedures to determine peak flows at locations downstream of a dam. Use of the prediction equation will improve the accuracy of rapid assessments of damage that would be caused by the flood resulting from an embankment dam failure.