Software application families and their accompanying architectures (also referred to as product line architectures or PLAs) are a promising area in which the potential of software component reuse can be fully realized. Evolving such application families necessitates making informed architectural decisions. Among industry and research communities, it is recognized that software metrics can provide guidance during the making of such decisions. In this paper, we introduce metrics that are specifically geared to assess product line architectures and help in maintaining their quality.