Ultrasonic transducer, which converts electrical energy to mechanical energy is one of the most important components of an ultrasonic welding machine. Similar ultrasonic transducers are used as sonars in medical applications and in ultrasonic cleaning devices. They differ in geometry of certain parts and operating frequency. Impedance characteristics of each transducer is very important for a proper operation of the transducer and for determination of its resonance frequency. In the literature review ultrasonic welding and piezoelectric materials, which enable the energy conversion are described. Also modelling of the ultrasonic transducer in Comsol Multiphysics software is described minutely. Experimental systems for measuring the impedance and strain amplitude are presented. We proved that the simulated and measured impedance characteristics are very well matched. It was established that the impedance characteristics, strain amplitude, location of longitudinal vibration node and resonance frequency are influenced by the mass and geometry of transducer elements. The computer model of the ultrasonic transducer can be used to predict how a manufactured transducer will work before it is even produced, which cuts down development costs.