The awareness of sustainability is increasing in diverse industries, including fashion industry. The second-hand clothing trade might be considered as a way to make apparel more sustainable. However, the second-hand market adds to the environment contamination using toxic elements to disinfect the clothing. Enhancing the lifespan of product by making it transformable is another approach to sustainability. Transformable modular clothing is one of the alternatives to reduce consumption. Thus, this paper aims to develop a modular garment construction as a way of forming the ready-made clothing by the consumer himself. While fashion depends on continuous updates, the proposed way of assembling the ready-made clothing as a modular item allows the garment to last emotionally long enough to be addressed practically by consumers. An example of modular clothing is designed based on the typological range of women clothing. The range consists of different garment types, which might be transformed into each other. The principle of universality was applied as a basic principle of modular garment design. The universal basic garment designs were found for several different combinations of garment types. The technical information needed to design the modular garment is represented in a form of database of transformation elements.