Electrical admittances have been measured for rectangular bars of barium titanate, lead zirconate‐titanate, and sodium potassium niobate which were poled in a direction normal to the driving electrodes. Resonant frequencies for the first eight modes of vibration have been determined from these measurements. A comprehensive survey has been made of 50 or more transducers of each material in a width‐to‐thickness (w/t) range from 0.2 to 100. The velocities for longitudinal waves in a thin rod and dilatational waves in an extended body have been determined from the value of frequency‐thickness (fRt) product at the limiting values ofw/t. Graphs show the dependence of electromechanical coupling andfRtonw/tover a range from 0.2 to 6. The results are compared to those for resonant vibrations in circular disks reported by Shaw. Graphical results show the optimum values of width and thickness dimensions for transducer design in the first mode and a technique for determining optimum dimensions for resonance in other modes is outlined. A normalizing parameter is introduced which is determined for a given material from a measurement offRin the first mode for a single transducer. For materials with Poisson's ratio between 0.2 and 0.4, this parameter permits the design of transducers to a frequency within ±3% in the first mode.