The competitiveness in today's market forces many companies to rethink the way they design (and redesign) products. Instead of developing one product at a time, many manufacturing companies are developing families of products to provide enough variety for the marketplace while keeping costs relatively low. Although the benefits of commonality are widely known, many companies are still not taking full advantage of it when developing new products or redesigning existing ones. One reason is the lack of appropriate methods and useful metrics to assess a product family based on commonality and diversity. Although many component-based commonality metrics have been proposed in the literature, they do not (1) help resolve the tradeoff between commonality and diversity in a product family and (2) capture enough information to be completely useful during product family design and redesign. In this paper, we propose the Comprehensive Metric for Commonality (CMC) to evaluate the design of a product family on a 0-1 scale based on the components in each product, their size, geometry, material, manufacturing process, assembly, costs, and the allowed diversity in a family. To demonstrate the usefulness of this metric for product family benchmarking and redesign, the CMC is compared to six other component-based commonality indices. A CMC-based method is also proposed and applied to a family of staplers to (1) assess the level of commonality in the product family and (2) give recommendations for redesigning the product family.