Body mass index (BMI) is a standard method for determining if you are carrying too much unhealthy weight. It is calculated by using your height in inches or meters, and by your weight in pounds or kilograms. For example, to calculate your BMI using inches and pounds, you would multiply your weight by 703, divide that answer by your height in inches, and than divide that answer by your height in inches again. Calculating your BMI can be helpful in determining whether you are overweight; however, it is not accurate with some populations.
Significance
Obesity is a leading risk factor for a variety of diseases, including heart disease, type 2 diabetes, certain cancers and high blood pressure. Heart disease, for example, kills more American adults each year, than any other cause of death.
Considerations
Your BMI calculation does not indicate your body fat percentage. However, according to the Centers for Disease Control and Prevention, CDC, your BMI correlates with direct methods of body fat testing, such as caliper testing and water immersion. A BMI of 18.5 to 24.9 is considered normal, while if your BMI is 30 or above, you are considered obese. To determine BMI, a person that weighs 215 lbs. and is 6 feet tall, would multiply 215 by 703. The result would be 151,145. Dividing 151,145 by 72, the result would be 2099.23. Finally, dividing 2099.23 by 72 again, would indicate a BMI of 29.15. If your BMI is 29.15, you are considered overweight.
Children
BMI is calculated using the same method with children as it is with adults. However, because a child's body fat differs according to age and sex, BMI calculations are adjusted by percentiles according to those factors. According to the National Institutes of Health, rather than trying to determine a child's BMI, you should have his physician determine if he is overweight for his age.
Reliability
With certain groups, BMI is not an accurate indicator of body composition. For example, with the same BMI, women tend to have more fat than men. Senior citizens also tend to have a higher fat percentage than younger people with the same BMI. Highly trained athletes may have a relatively high BMI, but in many cases, they have a high percentage of lean mass, and a low body fat percentage.
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