Product modularity is a design strategy that offers mutual benefits to the manufacturing companies. Its benefits can be varied from satisfying diverse customer needs through offering customized product with reduced lead-time. This research investigates the overall concept of product modularity, its application in industry and related works published in the literature. The main objective was to identify metrics can be used to measure product modularity. Six industrial cases are investigated in this research study with the objective to measure their product modularity levels. In order to measure such modularity level, Design Structure Matrix (DSM) tool and an analytical method are used. Result shows that overall modularity level in the case industries varies significantly based on product architectures, which are related to the number of components, number of modules, and number of interfaces/dependencies.