Mayo Clinic BMI and waist circumference calculator BMI is a measure of body mass. (BMI) is a calculation that utilizes height and weight to measure body fat. High BMI is associated with an increased risk of chronic diseases like heart disease, high blood pressure, and type 2 diabetes in adults. BMI can provide a fair estimate of body fat for most people. However, it's not without limitations. For instance, BMI may: Do not overestimate the body fat of seniors or those with lower muscle mass Overestimate body fat in people who are incredibly muscular and physically fit In addition, BMI may underestimate risk for people of Asian descent, in part because it does not take into account the risks posed by excess abdominal fat. Thus, it's important to consider waist size (measured just above the hipbones in individuals) alongside BMI. Health risks increase when waist size increases, regardless of BMI. Talk to your doctor should you have questions about yo...