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Body Mass Index

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The body mass index, or BMI, is used to estimate roughly how overweight or underweight someone is. A person's BMI is calculated by taking his weight (in kilograms) and dividing it by the square of his height in meters. The BMI can be calculated using other units of measurement, such as pounds and ounces and feet and inches, by applying correction factors to convert the measurements to the metric system.

The US Centers for Disease Control and Prevention uses the BMI to make rough recommendations on how your weight for your height may influence your health. For adults and older adolescents, BMIs of 19 to 25 are regarded as "average". A person with a BMI of 25 to 30 is considered overweight, while someone whose BMI is over 35 is considered obese. On the other end of the spectrum, a BMI of less than 18 may indicate malnutrition, and a BMI of less than 17.5 is one of the American Psychiatric Association's criteria for the diagnosis of anorexia nervosa.

As with weight, height, and the rate of change in each, average BMI ranges are different at different ages. Children in their preteen years have much lower average BMIs than do small children or adults. The CDC's National Center for Health Statistics, which publishes the standard growth charts that pediatricians use to keep track of how children are growing, also publishes standard curves for BMI in boys and girls younger than 18 years. We can use these curves to find out how a particular child's BMI compares to average; this information may alert us and our patients' parents to a possible obesity or anorexia problem much earlier than we might notice just by examiniation.

Again, the BMI is a rough estimate of weight and stature. Just looking at weight and height doesn't tell us whether the extra weight is from fat or muscle. Many trained athletes including football players have high BMIs, but their "extra bulk" tends to be muscular.

This calculator will take your weight and your height and compute your BMI. (JavaScript must be enabled in your browser for you to use this calculator.)

Body Mass Index Calculator

              ounces (use if entering pounds and ounces; otherwise leave blank)

 Severely underweight: BMI less than 17.5
 Normal range: BMI between 19 and 25
 Overweight: BMI between 25 and 30
 Obese: BMI over 30

 These definitions are based on recommendations from
 the US Centers for Disease Control and Prevention.

            inches (use if entering feet and inches; if entering inches, leave blank)

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PLEASE NOTE: As with all of this Web site, I try to give general answers to common questions my patients and their parents ask me in my (real) office. If you have specific questions about your child you must ask your child's regular doctor. No doctor can give completely accurate advice about a particular child without knowing and examining that child. I will be happy to try and answer general questions about children's health, but unless your child is a regular patient of mine I cannot give you specific advice.

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Copyright © 2007, 2009 Vinay N. Reddy, M.D. All rights reserved.
Written 02/01/07; last revised 06/06/09 counter