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Body mass index

 

Alternative Names

BMI

Information

A good way to determine if your weight is healthy for your height is to calculate your body mass index (BMI). Being overweight puts strain on your heart and can lead to serious health problems. These problems include:

More than 300,000 lives could be saved in the United States each year if everyone stayed at a healthy weight!

HOW TO DETERMINE YOUR BMI

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.

BMI CATEGORY
Below 18.5 Underweight
18.5 - 24.9 Healthy
25.0 - 29.9 Overweight
30.0 - 39.9 Obese
Over 40 Morbidly obese

BMI is not always an accurate way to determine whether you need to lose weight. Here are some exceptions:

  • Body builders: Because muscle weighs more than fat, people who are unusually 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 osteoporosis.
  • Children: While an alarming number of children are obese, do not use this BMI calculator for evaluating a child. Talk to your pediatrician about the appropriate weight for your child's age.

Doctors use a few different methods to determine whether you are overweight. Your doctor may also take your waist circumference and waist-to-hip ratio into consideration.

In addition, a lot of other factors influence your health. These include:

  • Blood pressure
  • Blood sugar levels
  • Cholesterol levels
  • Diet
  • Physical activity
  • Smoking

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 doctor before starting an exercise program.

References

Noel MB, Thompson M, Wadland WC, Holtrop JS. Nutrition and family medicine: In: Rakel R, ed. Textbook of Family Medicine. 7th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 48.

Skelton J. Overweight and obesity. In: Kliegman RM, Jenson HP, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 44.


Review Date: 8/22/2008
Reviewed By: Linda Vorvick, MD, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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