© 2022, Istanbul Teknik Universitesi, Faculty of Architecture. All Rights Reserved.Architectural design could be defined as a process in which the information about various aspects of a design object is produced at different stages, then shared between relevant stakeholders. For the early stages of the architectural design, in order to carry out an efficient and productive design process, and create comprehensive solutions to design problems, novel digital tools have to be developed. Digital become omnipresent in the contemporary architectural practice. Even though very complex design ideas could not be realized without the help of the Computer-aided Design (CAD) tools, some may argue that the idea generation is hindered by the employment of them during the early phases. With the idea of containing the essence of analogue tools, we propose an Augmented Reality (AR) application for architects to explore 3D mass geometries in a similar immediacy and ease of designing with a pen-paper. In this paper, we present and discus the validity of two chosen usability scales System Usability Scale (SUS) and Handheld Augmented Reality Usability Scale (HARUS) measuring comprehensibility of the developed AR application (MimAR). The results of the preliminary study shows that the chosen measurement methods provide a similar tendency of scores. The findings of this study suggests that the comprehensibility of the MimAR application still needs improvement, and yet the usability of the application could be considered above the acceptable threshold.