Technological advancements in electronics have greatly reduced power requirements. The piezoelectric transduction mechanism has received a great attention in the energy harvesting field. It is perceived by many researchers that using piezoelectric transduction, vibration based energy harvesting technique is the best candidate to meet low power requirements. Only recently, a revised and accurate mathematical model was proposed to predict the energy output from a cantilever energy harvester. In many applications, piezoelectric transduction can also be used to harvest the ambient vibration energy from plate type structures. A simple example is a host structure subjected to out of plane periodic vibration. In this paper, a mathematical model is proposed for a vibrating plate used as an energy harvester. Strain rate damping and viscous damping were considered separately in the dynamic equation. Complete dynamic equation for the coupled system is formulated. A solution mechanism is proposed under a harmonic loading condition to decouple the system. Modal analysis is performed under a short circuit condition and the solution from the transcendental equation is used to calculate the modal parameters. The backward coupling term is then calculated using the modal coefficients and the explicit equation for the voltage output is presented. A comparative study is presented to demonstrate the significant difference of ignoring the strain rate damping and adopting the damping in the model. It was fo und that for the plate type harvesters, strain rate damping was able to estimate the voltage output more accurately than the existing models.