Body Fat Estimate (YMCA formula) Calculator View Calculator This calculator uses the formula developed by the YMCA to estimate your body fat percentage without calipers. Use a tape measure and enter your waist measurement. Combine the waist measurement with your gender and weight and this calculator will estimate your percent of body fat, how much of your weight is lean mass and how much is fat mass, and your general fitness category. The water displacement test is the most accurate way to determine body fat percent, but the Navy Body Fat test or YMCA formula is accurate within 1-3% for most people. Learn more about putting this calculator or other calculators on your website.