Design for Manufacture and Assembly (DfMA) is an evolving topic in the Architecture, Engineering, and Construction (AEC) industry because of its time and cost reduction efficiency. However, it is a concept difficult to implement due to the scale of the ‘product’, a building. Hence, as a research topic, it is still very limited in terms of knowledge dissemination. On the other hand, Modular Construction (MC), based on industrial products, has gained significant recognition for its potential to improve adaptability, productivity, and sustainability. By bridging the gap between theoretical constructs and practical implementation in contemporary construction practices, this research aims to develop a comprehensive framework for evaluating modularity in construction projects through the DfMA methodology. DfMA is commonly used in the manufacturing industry, and by integrating it as a design method, this research highlights the methodology of connecting design and production as a core foundation for MC, aiming to find the MC design methodology based on DfMA. The study begins with an extensive literature review to extract fundamental modular construction design principles, formulating an effective theoretical structure. Then, DfMA is examined as a crucial tool for assessing modularity by optimizing design, manufacturing, and assembly processes. Employing case-oriented research, the study analyzes different projects from various periods and locations, which provides diverse insights into the construction of modular-based projects through the practical application of DfMA. The study concludes by establishing a systematic approach to evaluating modularity, supporting the shift of the construction industry toward more innovative, optimized, and sustainable construction methods.