The thermoelectric generator (TEG) output power is mainly dependent on physical characteristics, dimensions, leg configuration, number of p-n thermocouples, and other parameters. Therefore, identifying the optimal leg configuration that attains the best performance is essential. The present work considers several leg configurations by the volume reduction of the conventional prism leg, without changing the shape class via decreasing basic dimensions (i.e. leg height or cross-sectional area) and with morphing the original prism into X and trapezoidal shapes. A three-dimensional thermo-electric model is developed to investigate the performance of TEG legs at the uni-thermocouple level. Besides, to determine the reliability of the proposed configurations, a wide range of thermal boundary conditions are applied on the hot side to resemble the realistic working environment that TEG might experience at room temperature on the cold side with natural convective cooling. The model is numerically simulated after being validated with the available experimental and numerical data. The comparison indicates that decreasing leg height adversely affects the TEG performance, whereas a significant enhancement in the performance is achieved (in order) for X, trapezoidal and reduced area shapes. However, the performance enhancement, i.e. power and efficiency, associated with the simple reduced area configuration is relatively close to those achieved by X or trapezoidal ones, raising many questions in terms of simplicity and manufacturing cost. The performed research further deepens our understanding of TEG performance enhancement via optimizing legs’ attributes at uni-thermocouple as a single building block of the full-size TEG module.