Your BMI estimates how much you should weigh, based on your height. Here are the steps to calculate it:
Multiply your weight in pounds by 703.
Divide that answer by your height in inches.
Divide that answer by your height in inches again.
For example, a woman who weighs 270 pounds and is 68 inches tall has a BMI of 41.0.
Use the chart below to see what category your BMI falls into, and whether you need to be concerned about your weight.
18.5 - 24.9
25.0 - 29.9
30.0 - 39.9
Extreme or high risk obesity
BMI is not always the best way to decide whether you need to lose weight. If you have more or less muscle than is normal, your BMI may not be a perfect measure of how much body fat you have:
Body builders: Because muscle weighs more than fat, people who are very muscular may have a high BMI.
Elderly: In the elderly it is often better to have a BMI between 25 and 27, rather than under 25. If you are older than 65, for example, a slightly higher BMI may help protect you from thinning of the bones (osteoporosis).
Children: While an alarming number of children are obese, do not use this BMI calculator for evaluating a child. Talk to your child's doctor or nurse about the appropriate weight for your child's age.
Health care providers use a few methods to decide whether you are overweight. Your health care provider may also take your waist circumference and waist-to-hip ratio into consideration.
Your BMI alone cannot predict your health risk, but most experts say that a BMI greater than 30 (obesity) is unhealthy. No matter what your BMI is, exercise can help reduce your risk of heart disease and diabetes. Remember to always ask your health care provider before starting an exercise program.
Gahagan S. Overweight and obesity. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 44.
Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.