As a result of the increasing number of electronic devices and limited space on aircraft, the development of high-efficiency and small-sized power supply systems is necessary. The switched tank modular converter (STM) receives attention recently because of its high power density and efficiency, which is suitable for aircraft application. Full soft charging is achieved by connecting a small inductor in series with the flying capacitor compared to the traditional switched capacitor (SC). Zero current switching (ZCS) helps to reducing the power loss of the switches. However, further reduction of the overall size is hampered by the fact that the effect of switches and passive components on the total volume is unclear. In order to find the optimum total volume of the STM, a comprehensive volume modeling and optimization method is proposed in this paper based on the semiconductor power loss and resonant capacitor voltage ripple analysis. A 12V-6V, 10W, 3.85MHz STM prototype is fabricated to verify the proposed optimization method, which achieves 96% peak efficiency at rated power and 51.25 mm³ total volume. Three groups of switches and passive components collocation are designed and the optimum volume group is found while remaining the highest efficiency.