Transducers as a heart of ultrasonic heads are one of the most important parts of systems. Among them, sandwiching, adhesive and screw transducers are more applicable, so the applications of ultrasonic waves will widely improve if they are designed correctly. The calculations of dimensions, especially the lengths of pieces, are very important in transducer designing because even a very small miscalculation causes differences in vibration conditions, and afterwards, decreasing or appliance malfunctions will result. The differential equation of the longitudinal vibration mode with its boundary conditions is solved to determine the length of the transducer. After that, the transducer is modeled with the finite element method to evaluate the theoretical calculations, and their resonance frequency is also determined by modal analysis. Finally a prototype transducer is manufactured and tested. The results of theoretical, finite element modeling and experimental tests are very close to each other, so this method was found to be a suitable base for transducer designing.