BMI Criteria

Body Mass Index (BMI) is a number that is calculated from an individual's height and weight. Unlike direct measures of body fat like underwater weighing, BMI measures body fat indirectly. It is a simple, economical gauge to identify weight issues that may pose health risks.

Calculation

• Divide weight in pounds by height in inches, squared. Then multiply by 703. For example, if your weight is 120 pounds and you are 5'8" tall (68"), then the equation should be 120 divided by 68 squared times 703, equaling 18.24.

  If you're using the metric system, BMI is calculated by dividing weight in kilograms by height in meters, squared. (Divide centimeters by 100 to get height in meters.) For example, if you weigh 72 kilograms and are 170 centimeters tall, your equation should be 72 divided by 1.7 squared, equaling 24.91.

  The BMI calculation is the same for children and adults.

Interpretation

• Standard weight status categories are used to interpret BMI for men and women older than 20. BMI ranges for adults are as follows: below 18.5, underweight; between 18.5 and 24.9, normal; between 25.0 and 29.9, overweight; and 30.0 and above, obese.

Controversy

• BMI fails to distinguish between fatty and lean tissue, thus it remains an imprecise measure of fat in individuals. A 270-pound football player may be solid muscle with low body fat, but he would be considered obese according to his BMI. According to the National Institutes of Health and the World Health Organization, degree of body fatness is a more effective way to categorize individuals.