Abstract: Dual resonator crystal filters have an input electrode, a common electrode, and an output electrode which provide two resonators coupled together. Mathematical formulas were derived to determine the resonator frequencies, the synchronous peak separation frequency, and the normalized center frequency. These formulas use selected frequencies or parameters which can be easily measured by applying a variable band of frequencies to the input electrode of a dual crystal filter. Measurements are made of the frequencies at which the voltage at the common electrode is a maximum when the output electrode is connected to the common electrode by capacity and when the output electrode is connected to the common electrode by a short circuit. The measured frequencies can be used in the mathematical formulas to determine the resonator frequencies, the synchronous peak separation frequency, and the normalized center frequency.