For many thickness‐drive transducer applications, it is desirable to have a good estimate of the radiation conductance (or other property based on power output) of the transducer. Generally,however, it is difficult to measure directly transducer power output. It is therefore desirable to have a procedure for estimating radiation conductance from easily measured quantities. Themeasured quantities used in this paper are electrical admittances at the terminals of thetransducer when it is in air, and when in water. The transducer model used to interpret the measured admittance is a lumped‐constant equivalent circuit; it hasbeen refined to represent an electrically excited thickness‐drive transducer over the frequency range 0.5–40 MHz. Two methods are used to estimate radiation conductanceGrad(f), and efficiency. One, the general‐case method, gives values ofGradover a wide range of frequencies, the other gives values ofGradonly for the special case in which the transducer is at a half‐wave resonance. For the general case, a novelprocedure, similar to iterative optimization, is used to estimate parameters for the equivalent circuit. Provision is made for estimating a tuning‐coil resistance that isfrequency dependent. The validity of the two methods is tested by comparing resultantGrad(f) values with those measured by the National Institute of Standards and Technology (formerly National Bureau of Standards). The maximumdiscrepancy at the lowest transducer resonance is approximately 15% for the small number of transducers on which measurements have at present been made. The transducers studiedherein have active elements with characteristic impedance much higher than that of water.Polymer‐film transducers are not considered.