The upcoming circular economy has consequences for the application of materials within the building sector, which requires a different mindset and way of designing from the architect. The aim of this research is to develop a Circularity Overview in which the materials of a building can be assessed for circularity and environmental impact. The Overview can thus be used as a tool to test materials of an existing building, materials for a design, or can be used as a tool during the design process for adaptive reuse. This allows for orderly weighing of options and making choices, therefore it is a tool that can be of interest to students and architects who will be working with circular material use. The Overview is developed from criteria that have been compiled through desk research, for which it was important that the criteria are measurable and verifiable so that results can be replicated and traced. Knowledge about circularity was generated through literature research, after which six case studies were analyzed with an objective view. By testing the Overview on both newly built circular projects and transformed buildings, it emerged that the combination of material use and construction technique of both, such as reusing materials, applying detachable connections, and keeping existing structures intact as much as possible, can lead to favorable outcomes in terms of circularity. The circularity of the case studies as well as the operation of the Overview itself have also become insightful as a result. Although the Circularity Overview has shortcomings due to the incomplete availability of data, it provides an indication of circularity in material use that can be used to support choices before, during, and after a design phase. The Circularity Overview was used during the design process for the revitalization of the St Barbara church in Culemborg, which resulted in a design with minimal impact on the environment.