The notion of maximizing software reuse among the family of products has gained considerable attention in the last decade. Lots of research has been done on designing and managing the commonalities and variabilities between the products. However, very few metrics have been developed to assist architects in designing product line architectures. The structure of the product line holds immense importance towards increasing the life span of the product line. Since many of the product line architecture design methodologies follow a component based approach, it seems logical to attempt to adapt the component based metrics to the product line domain. In this thesis, we attempt to derive metrics that quantify the structural quality of product line architecture.