Designers and design researchers use multiple metrics to evaluate prototypes. However, no single study synthesizes metrics that can be used to evaluate prototypes. The objectives of this research are: (I) to identify and synthesize metrics to evaluate physical prototypes from literature (constitutes theoretical perspective) and practitioners (constitutes empirical perspective), and (II) to compare the theoretical and empirical perspectives. The metrics are identified through a systematic review of literature shortlisted using the PRISMA framework and an online survey to collect the opinions of practitioners of various levels of experience. The identified metrics from the literature are categorized into: (a) 14 categories (appearance, assembly fit, cost, ergonomics, functionality, geometry, maintainability, manufacturability, originality, part count, performance, physical properties, time, and user interaction and experience) based on their definition, and (b) 16 categories (AM/3D-printers, cardboard, clay, CNC, foam, junk modeling, hand tools, laser cutter, LEGO kits, metallic, conventional machining, mixed reality with physical prototype, molding, paper, ply or rubber wood, and plastic/PVC) based on the prototyping tool. The identified metrics from the empirical study are categorized into 7 categories (appearance, cost, ergonomics, functionality, geometry, manufacturability, and user interaction and experience) based on their definition. The differences in the findings of the theoretical and empirical perspectives signify the possibility for the practitioners to consider more metrics to evaluate their prototypes to ensure the prototypes are thorough and robust. This calls for support to help practitioners to choose metrics relevant for their prototyping context from an encompassing list.