Market differentiation strategies must identify competitive advantages when offering a line of products varying in features, price, quality, and/or aesthetics. Although this concept is well-known, many companies still have difficulties positioning their own products within their own product lines and against competitors. Few approaches combine two or more facets to answer the product differentiation problem. In this study, two novel indices are proposed to audit shape and functional differentiation within a family of products. The shape index appraises the shape similarity between the products upon digitization, while the functional assessment is based on functions characteristics of the product. Customers' perception data is obtained experimentally and compared to these indices to validate the result. Pairs of products are evaluated, and the average scores are considered as the indices for a product family. A case study illustrates the usage of these two indices and performance of these tools as well. This approach can be used during detailed studies as well as early stages of the design process to help validate product family positioning.