Wave energy converters (WECs) often employ submerged heave plates to provide reaction forces at depths below the level of wave motion. Here, two sets of heave plate experiments are described, at varying scale. First, the Oscillator uses a linear actuator to force laboratory scale (30.5-cm diameter) heave plates in sinusoidal motion. Second, the miniWEC buoy uses vessel wakes to force field scale (1.5-m diameter) heave plates in open water with realistic energy conversion (damping). The motion and forces are analyzed using the Morison equation, in which the hydrodynamic coefficients of added mass CM and drag CD are determined for each set of Oscillator and miniWEC experiments. Results show strong intracycle variations in these coefficients, yet constant hydrodynamic coefficients provide a reasonable reconstruction of the time series data. The two test scales are examined relative to the Keulegan-Carpenter number (KC), Reynold's number (Re), and Beta number (β). The effects of asymmetric shape on hydrodynamic performance are found to be small.