In this chapter, the main dimensions of transformer windings are determined by applying the essential principles and methodologies. Finally, it provides a complete design approach taking into consideration both core type and shell type of single-phase and three-phase transformers. Geometries of core, including total height (H), total width (W), and the distance between adjacent limbs (D), are discussed in the context of what influence it has on the winding configuration. The chapter discusses critical dimensions like the diameter circumscribing circle (d), window width (Ww), window height (Hw), yoke height (Hy), and yoke depth (Dy) as these are important for the performance, cooling and mechanical strength of the winding assembly. The review includes various winding types (cylindrical, helical, continuous disk, and layer windings) and emphasizes construction, applications, and suitability for voltage level and transformer rating. Electrical, thermal as well as mechanical stresses are analyzed based on the choice of winding. The chapter brings out the fact that proper dimensioning is important for proper insulation coordination and loss minimization. Detailed solutions for numerically computed cases are given, illustrating practical design methods for determining most of the main parameters. Finally, this chapter offers a foundation for the design of safe and economically advantageous winding that is a prerequisite for transformer reliability and cost-effectiveness as well as operational efficiency.