The purpose of this paper is to provide a frame work for approaching a power analysis for a CRT (cluster randomized trial) with a binary outcome. The authors suggest a framework in the context of a simple CRT and then extend it to a blocked design, or a multi-site cluster randomized trial (MSCRT). The framework is based on proportions, an intuitive parameter when the outcome is binary. In addition, they provide sample power tables to provide readers with some intuition regarding sample sizes for CRTs with binary outcomes. (Contains 1 figure, 1 table, and 2 footnotes.)