In the design process of a practical power converter, a designer considers not only the electrical input/output performance criteria which the converter is supposed to meet, but also efficiency and overall volume. Mostly, factors that strongly affect efficiency and converter volume such as choice of switching frequency (f) and the amount of inductance (L), are solely selected depending on the designer's former experience and/or widely accepted rules of thumb, without any serious calculation. This study aims to show an efficiency and volume optimization based design process of a 1 kW step-down dc/dc converter. Effects of changing f and L value on system's overall efficiency and volume will be shown and an optimum design point will be reached. Also the phase number (N) is considered as an optimization parameter.