The efficiency of energy conversion by piezoelectric devices depends upon the quality factor Q and electromechanical coupling coefficient k2. In this study the efficiency Q and k2 are measured for a piezoelectric cantilever, a piezoelectric stack, and a micromachined piezoelectric membrane. The experimental values are compared to a model which predicts efficiency at resonance in terms of k2 and Q. Results of the experiment and model are within 2% of each other.