# Calculating your body mass index (BMI)

Sep 28, 2007 at 9:29 p.m. ET

Health professionals use a measurement called body mass index (BMI) to classify an adult's weight as healthy, overweight, or obese. BMI describes body weight relative to height, and is correlated with total body fat content in most adults -- both men and women.

You can calculate your BMI using these three simple steps:

1. Multiply your weight in pounds by 703.
2. Next, divide the result by your height in inches.
3. Then, divide that result by your height in inches a second time.

The value you get will put you in one of four BMI categories: underweight, normal weight, overweight, or obese.

### BMI categories

"Overweight" refers to an excess of body weight, but not necessarily body fat. "Obesity," on the other hand, means an excessively high proportion of body fat.

Here are the general BMI scores:

• Underweight:
• Normal weight: 18.5 to 24.9 percent
• Overweight: 25 to 29.9 percent
• Obese: BMI of 30 percent or greater

### Limitations of the BMI

BMI is a reliable indicator of total body fat, which is related to the many health risks. The score you receive is valid for both women and men -- but it does have some limits. For example:

• It may overestimate body fat in athletes and others who have a muscular build.
• It may underestimate body fat in older persons and others who have lost muscle mass.

### More on the BMI

A BMI from 18.5 up to 25 is considered in the healthy range, from 25 up to 30 is overweight, and 30 or higher is obese. Generally, the higher a person's BMI, the greater the risk for health problems, according to the National Heart, Lung and Blood Institute (NHLBI). However, there are some exceptions. For example, very muscular people (such as body builders) may have a BMI greater than 25 or even 30, but this reflects increased muscle rather than fat.