The objective of this research is to develop and validate a framework of metrics for physical and virtual prototypes of physical products. The framework is intended to help designers identify relevant metrics comprising multiple evaluation aspects to ensure comprehensive evaluation of prototypes. This framework employs the criteria of kind of prototype, prototyping tool, and evaluation category to select relevant metrics from an encompassing list. It provides flexibility to users starting with any criteria. The concepts of the framework are implemented into a web-based interactive application as a tool for users. The framework is validated for usability and utility through an empirical study involving 31 design students. The students are instructed to identify metrics to evaluate a given prototype, first without and next with the framework, and respond to a questionnaire comprising questions from the System Usability Scale (SUS) and some open-ended questions. The number of metrics and evaluation aspects identified with the framework are significantly higher than without the framework, signifying the utility of the framework. The distribution of SUS scores signifies that the framework is user-friendly, easy to use, functions are well integrated, and it helps to identify metrics quickly and efficiently, suggesting frequent use of it.