The ultrasonic pulse-echo technique of ultrasonic gages is used to measure the thickness of coatings on non-metal substrates (wood, concrete, plastics, composites, etc.) without damaging the coating. An ultrasonic transducer emits a high frequency sound pulse that travels into the coating via a coupling gel and reflects from ANY surface that is different in density. Coating thickness readings are obtained by measuring the time taken for the ultrasonic signal to propagate from the probe to the coating/substrate interface and back. The travel time is divided by two and multiplied by the velocity of sound in the coating to obtain the thickness of the coating. In some circumstances, individual layers in a multi-layer system can be measured.