**This page has the latest version of the study protocol for conducting the focus groups.** **Title** Measuring cannabis use quantities in surveys: a study protocol for developing the CannaQuant survey tool **Version** 1 **Date** 22 February 2023 **Authors** Jakob Manthey, Arto Arman, Mercè Balcells-Oliveró, Andreas Beerli, Alain Cohn, Pablo Guzman, Aljosha Henkel, Michel André Maréchal, Esther Neumeier, Clara Oliveras, Maite Pons-Cabrera, Moritz Rosenkranz, Philipp Sternal, Hugo López-Pelayo **Abstract** Cannabis is the third most consumed drug globally and is legally available to an increasing number of people. The heterogeneity in cannabis use practices and cannabis products is prohibiting a straightforward assessment of cannabis use amounts. There are currently no standards to collect information on cannabis use amounts through self-report. This research aims to develop a brief culturally adapted cannabis quantity measurement module for surveys (in short: CannaQuant survey module) for 3 European countries (Switzerland, Germany, Spain). Specifically, we will develop survey items accompanied by visual aids that can be used by current cannabis users to estimate their use amounts separately for cannabis flowers and resin. For this purpose, we will conduct focus group studies with cannabis users from Germany, Spain, and Switzerland (n=10 users per country; 4-6 users per group). In the focus groups, discussion among users on various aspects of cannabis use amounts will be facilitated. The primary outcome of each focus group is to develop draft visual aids for both cannabis flowers and resin, that can accompany a survey item for estimating usual use amounts. Through guided discussions, the focus groups will reflect on different experiences with dosing and product choices. The items developed in the focus groups will be made publicly available to facilitate the measurement of cannabis use quantities through self-report, e.g., in future general population surveys but also in clinical practice.