Concrete masonry units sampled at the jobsite never are tested for aggregate type by a third party because the cost of testing is prohibitive. But there is a cost-effective way to assess CMU fire resistance. The article, which includes three tables, provides a simple density procedure for a quick and easy field check of manufacturers' claims: 1. Weigh an air-dry concrete masonry unit on a good bathroom scale. 2. Estimate the concrete volume and equivalent thickness using Table 2 (in the article), "Equivalent Thickness and Concrete Volume in Loadbearing Hollow Concrete Masonry Units." 3. Divide the weight by the volume to estimate the maximum air-dry density of the concrete. 4. Subtract 2.5 pounds per cubic foot to estimate the oven-dry density. 5. Estimate the CMU fire resistance for Table 2 (in the article), "Minimum Equivalent Thickness of Concrete Masonry in Inches." The bathroom-scale method for estimating CMU fire resistance is based on an analysis of 153 fire tests on concrete masonry walls, representing nine different types of aggregate. These tests followed ASTM E 119 Standard Fire Test Method for Walls.