The key to defining a good platform is to identify the common modules that will be shared among products. We develop a quantitative algorithm to identify common sets of elements within a product, as well as, across products. We show a quantitative way of measuring module commonality. We specify commonality based on a Euclidean distance that compares different modules' inputs and outputs. We cluster modules based on their measured commonality and use dendrograms as a tool to identify groups of similar modules in a product family at the architectural phase of product design. We present the results of the application of our method on a hypothetical example and a real case study. © 2008 Springer-Verlag London Limited.