The effects of reversible and irreversible switching processes on the electromechanical large-signal strain S of tetragonal Pb(Zrx,Ti1-x)O3 thin films are investigated and discussed. Starting from electric small- and large-signal measurements, the percentage of switched unit cells cesw is calculated. The result is then used in combination with the measured electromechanical field-induced small-signal response to calculate the field-induced large-signal strain S. Enhanced models for this calculation are developed improving a known model. Differences between the calculated and measured large-signal strains are discussed in respect to parameter influences and irreversible contributions. In addition, detailed insight on the switching processes in respect to the electromechanical properties is given.