The generation of electricity from vibrations has attracted considerable attention over the past decade. For this purpose, a piezoelectric-type harvester tuned to resonate at a specific frequency is typically used. This paper proposes a SPICE model capable of modeling piezoelectric energy harvesters. The model is parametrized enabling simple introduction of relevant physical parameters. Underlying theory based on Euler-Bernoulli beam theory is presented and modeling simplifications are justified. The SPICE model is verified by comparison to examples for which analytical and experimental solutions has been published. The SPICE model is valid close to the analyzed mode center frequency and delivers results within 1% compared to experimental and analytical data. Furthermore, we also show that the harvester can be electrically tuned to match the excitation frequency. This makes it possible to maximize the power output for both linear and non-linear loads. The here presented model enables efficient analysis of harvester design and changes of harvesting conditions.