Body Mass Index (BMI)

Body Mass Index (BMI) measures your body weight relative to your height. Your doctor may use BMI to learn the proportion of fat to muscle in your body (people with a higher proportion of fat tend to have a higher BMI) and to determine if you are underweight, normal weight, overweight or obese.

“BMI can help you and your doctor determine whether you’re at risk of developing health problems such as diabetes and heart disease from excess fat and weight,” says family medicine physician Sean Heffelfinger, M.D., of Lehigh Valley Hospital and Health Network. BMI is determined differently for adults and children.

Adult BMI

If you are 20 or older, calculate your BMI using this formula:

Multiply your weight in pounds by 703.
Divide the result by your height in inches.
Divide that result by your height in inches.
For example, a person who weighs 140 pounds and is 65 inches tall has a BMI of 23.4.

BMI Results:

Less than 18.5: Underweight
Between 18.5 and 24.9: Healthy weight
Between 25 and 29.9: Overweight
At or greater than 30: Obese

Children’s BMI

If your child is in the 95th percentile, it means she is heavier than 95 percent of children her age. To easily calculate your child’s BMI, click on the related link below.

BMI Results:

At or over 95th percentile: Obese
Between 85 and 95th percentile: At risk for being overweight
Between 15th and 85th percentile: Probably at a healthy weight
Between 5th and 15th percentile: Possibly for risk of underweight
Under the 5th percentile: Underweight

It is important to be aware that BMI is not an appropriate measure for persons who are trained athletes or body builders.

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