When discussing weight with your doctor, you may hear the term BMI. He may suggest lowering your BMI, which is your body mass index. In the fitness world, you may hear the term body-fat percentage. These terms are often confused and thought to be interchangeable, but they are two different concepts.
BMI
BMI is calculated by dividing your weight in kilograms by your height in meters. It is often used in charts that indicate your ideal weight based on height. Other weight charts can take gender into consideration, but BMI does not consider gender.
Advantages
BMI is easy to calculate and can be done by anyone. You start by dividing your weight by 2.2 to convert to kilograms. Next, multiply your height in inches by 0.0254 to convert to meters. Divide your weight in kilograms by your height in meters to calculate your BMI. On the BMI chart, less than 18.5 percent is underweight, 18.5 to 24.9 is normal, 25 to 29.9 is overweight and above 30 is considered obese.
Disadvantages
BMI does not always apply to athletes. A muscular athlete with a higher body weight, compared to a nonathlete of the same height, may fall into the obese category when he is not even overweight.
Body-Fat Percentage
Body-fat percentage measures the ratio of fat mass to lean mass. Fat mass is adipose tissue, intramuscular fat and subcutaneous fat. Lean mass consists of lean muscle, bones and anything else in the body that is not fat.
Advantages
Body fat is a measure of your body's composition and a better gauge of overall health, since excessive fat can predispose you to metabolic disorders. It can be used with any population and is based on the individual and not just height and weight.
Disadvantages
Body fat is not based on a simple calculation such as BMI and is harder to obtain. One of the best methods of measuring body fat is hydrostatic weighing, which requires expensive equipment and is not easily accessible to everyone. Skin-fold calipers can be used, but they also require an individual to perform the measurement.
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