Piezoelectric DC-DC converters operate between the series and parallel frequencies of the piezoelectric resonator to achieve soft switching and energy-balance conditions. This letter presents an experimentally validated model to accurately predict the operating frequency, the switching angles and the piezoelectric current for any 6-phases piezoelectric DC-DC converter. This model reduces the transient simulation's calculation time to reach steady state. It can be used to initially setup the switching angles in experiment, or to predict the high frequency spectrum generated by the converter cycle.