Understanding Your BMI

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Your Body Mass Index (BMI) is a number calculated from your weight and height. Although BMI does not measure body fat directly, research has shown that BMI is a reliable indicator of body fatness for people, and it correlates to more high-tech measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry (DXA). BMI has the added advantage of being inexpensive and easy to perform. This number can help your physician identify possible weight problems.

How Can You Calculate Your BMI?

If you want to calculate your own BMI, follow these guidelines:

Using the Metric System
With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters:

BMI = Weight ÷ height²

Example: Height = 165 cm (1.65 m), Weight = 68 kg

Calculation: 68 ÷ (1.65)² = 24.98

Using Pounds and Inches
To calculate BMI using pounds and inches, you divide your weight in pounds by height in inches squared, then multiply by a conversion factor of 703.

BMI = Weight ÷ height² x 703

Example: Weight = 150 lbs, Height = 5'5" (65")

Calculation: [150 ÷ (65)²] x 703 = 24.96

What If I Don't Want to Do the Math?
If you want to use an easy calculator to determine your BMI, go to the website for the Centers for Disease Control, which provides an online calculator at:

www.cdc.gov/nccdphp/dnpa/bmi/adult_BMI/english_bmi_calculator/bmi_calculator.htm

How Do I Interpret My BMI?

For adults 20 years old and older, you interpret the results of your BMI calculations by using standard weight status categories that are the same for all ages and for both men and women.

(Note: calculating and interpreting BMI results for children and teens is a different process. If you need information and guidance about calculations for someone under the age of 20, visit the Centers for Disease Control website at this address: http://apps.nccd.cdc.gov/dnpabmi/Calculator.aspx)

The standard weight status categories associated with BMI ranges for adults are shown in the following table.

Below 18.5 — Underweight
18.5 - 24.9 — Normal
25.0 - 29.9 — Overweight
30.0 and Above — Obese

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