A key phase in product design and development processes is the establishment of product architectures. During this phase, functional models are transformed into alternative product layouts. In this paper, we introduce a methodology for representing a functional model of a product in a quantitative manner. The quantitative functional model captures product functionality and customer need information. Repositories can be created which house product design knowledge for a vast number of products using this novel representation. Numerical manipulations of such a repository assist in developing product architectures. In particular, product families and aggregate customer need ratings for modules are easily computed. Also, the quantitative functional model provides a mechanism to archive and transmit design knowledge across time and space. Prior to presentation of the methodology, a review of customer needs gathering techniques and module identification methods is given. Results from a repository of 70 consumer products are presented to illustrate the utility of the quantitative functional model.