Transformer design is vital in advancing electrical engineering in terms of performance improvement, reducing operational cost, as well as energy efficiency. This chapter offers a systematic approach to transformer design optimization based on accurate estimation of no-load current, core losses, core volume, and weight. The parameters are interrelated and have a great influence on transformer efficiency, cost of manufacturing, and durability. The relationships between key design variables such as core material characteristics, winding configurations, and geometric dimensions are established precisely through the combination of analytical and numerical methods. Core magnetization is analyzed in order to evaluate no-load current which accounts for hysteresis and eddy current losses. Standard performance criteria are used to minimize these losses to be realized by selecting core materials with high permeability and low loss factors. An optimization is made of the core volume and mass in order to achieve desired power ratings with reduced thermal and structural efficiencies. It is shown that this optimized design approach successfully reduces core losses and no-load current to lower the transformer’s size and weight. Therefore, this methodology could support the development of high performance and economical transformers, the potential further improvement of which is enabled by the use of advanced materials and novel cooling technologies to make a more sustainable, more efficient power systems.