The body mass index, or BMI, is a number derived from a person's height and weight. The Centers for Disease Control and Prevention says the BMI is a good gauge of a person's body fat percentage.
The Formula
The BMI formula is as follows: Divide your weight in pounds by your height in inches squared, then multiply that number by 703. Several free online calculators are available.
The Results
A BMI below 18.5 is considered underweight. A healthy weight falls in the 18.5 to 24.9 range. Adults with a BMI of 25.0 to 29.9 are considered overweight, and those with a BMI of more than 30 are considered obese.
BMI and Gender
According to the CDC, the average BMI is on the rise. In 1960, the average male BMI was a healthy 25.1. In 2002, the latest year that data were available, the average was 27.8. For women, the average BMI in 1960 was 24.9. In 2002, female BMI rose to 28.2.
Limitations
The formula does not take gender into consideration. According to the CDC, women tend to have a higher percentage of body fat than men do. Older adults with the same BMI of younger adults tend to have more body fat as well. The calculations do not evaluate percentage body fat versus lean muscle tissue, which may skew the BMI of athletes.
BMI and Weight Loss
The BMI can be combined with a Daily Needs Calculator (see Resources below) to help determine the number of calories your body requires each day to maintain current weight. A user is asked to input height and weight, as well as age, gender and level of daily activity. Learning how many calories a person needs to maintain his current weight is a valuable tool in the battle to lose weight.
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