The majority of existing commercial thermoelectric modules have fixed geometry, with customers purchasing those modules without adjusting its geometry for a specific application. However, previous investigations show that thermoelectric module geometry can have a significant influence on its output power careful design considerations are therefore required. In this study, both simulation and experimental investigations are conducted to optimize the geometry of thermoelectric modules, in order to achieve higher power while maintaining the cost low. The experimental setup is built, and three thermoelectric modules with different geometries but same material are tested. The documented experimental results agree well with the simulation results. Based on parametric studies, optimal thermoelectric module height to achieve maximum output power is found to be 1.1 min at the given thermal condition, slightly lower compared with the value used for most commercial products, which are around 1.5 mm. The effect of geometry design parameters on efficiency and power per material cost are also discussed, and the optimal design parameters are identified. Further improvements are proposed based on the simulation and experimental results.