**Calculate a person's BMI by dividing his weight in pounds by his height in inches squared.** Because the original calculations for BMI were done using the metric system, it is necessary to multiply the result by 703 in order to get the correct measurement.

BMI stands for body mass index. The normal range is considered to be between 18.5 and 24.9. A BMI below this range indicates that a person is underweight; a BMI above 24.9 means that a person is overweight. A

BMI above 30 indicates obesity. This is a useful measurement for tracking a person’s weight gain or loss and is often used together with the skinfold test to evaluate a person’s physical fitness, according to the CDC.

The same formula is used to calculate BMI in children and adults. However, the definitions of normal weight, underweight and overweight are different for children up to the age of 19, according to the CDC. Doctors compare children to others of their own age and gender to determine whether they are overweight, underweight or normal weight. This system defines children as being obese if they weigh more than 95 percent of their peers.