Body Mass Index Calculator What is BMI? Body Mass Index (BMI) is a number calculated from a person’s weight and height. BMI is a fairly reliable indicator of body fat for most people. BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry (DXA). BMI can be considered an alternative for direct measures of body fat. Additionally, BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems. How is BMI used? BMI is used as a screening tool to identify possible weight problems for adults. However, BMI is not a diagnostic tool. For example, a person may have a high BMI. However, to determine if excess weight is a health risk, a healthcare provider would need to perform further assessments. These assessments might include skinfold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings. Why is used BMI to measure overweight and obesity? Calculating BMI is one of the best methods for determining if you are overweight and/or obese. Because calculation requires only height and weight, it is inexpensive and easy to use for clinicians and for the general public. The use of BMI allows people to compare their own weight status to that of the general population. This calculator provides BMI and the corresponding weight category and is for adults 20 years and older.