Calculating Body Mass Index

The Body Mass Index (BMI) is a tool to indicate how much body fat a person has. It does not measure body fat directly, but correlates to more precise measurements of body fat.

Many health professional use BMI as an easy way to determine whether a person is overweight or obese, which could indicate possible health risks.

The Formula:

1. Measure your height in inches.
Example: The average American woman is 5 feet, 4 inches tall. That's 64 inches.

2. Square the height measurement (multiply your height by you height).
Example: 64 inches squared is 64 times 64, which equals 4,096.

3. Measure your weight in pounds.
Example: The average American woman weighs 164 pounds.

4. Divide your weight by the height squared.
Example: 164 pounds divided by 4,096 equals 0.040039.

5. Then multiply that number by 703.
Example: 0.040039 times 703 equals 28.15 (rounded up).

6. That is your Body Mass Index. Compare it to the chart below.
Example: The average American woman has a BMI of 28.

What The BMI Means:

Standard BMI calculations use the same weight statue categories for male and female adults 20 years and older.

Underweight is a BMI below 18.5.
Normal is a BMI between 18.5 and 24.9.
Overweight is a BMI between 25 and 29.9.
Obese is a BMI of 30 or higher.

Example: The average American woman is overweight.

For children and teens, the formula is the same, but the interpretation is specific to both age and sex. Any BMI measurements should be used in consultation with growth percentile charts. Those charts and more information can be found on the Centers for Disease Control and Prevention website.

Information adapted from the Centers for Disease Control and Prevention.