Body mass index is a number that is calculated from your weight and height. BMI is considered a reliable indicator of how much fat your body contains, according to the Centers for Disease Control and Prevention. While your BMI does not measure the amount of fat your body has directly, it correlates very closely with the measurements of fat made through other more direct and expensive methods.
Normal Body Mass Index
The normal range of the body mass index is from 18.5 to 24.99, the World Health Organization reports. While the BMI is independent of age and is the same for both genders, the concentration of body fat may not be the same in different populations because of different body proportions. Because of this, there has been some debate about the need to develop different cut-off points for different ethnic populations.
Calculating Your Body Mass Index
To get your BMI, simply multiply your weight in pounds by 703 and divide the product by the square of your height in inches, according to the Weight-control Information Network. For example, if you are 6 feet tall and weigh 220 lbs., you multiply 220 by 703 and get 154,660. Converting 6 feet to inches yields 72 and squaring that gives 5,184. Dividing 154,660 by 5,184 yields a BMI of 29.83. The calculation is simpler if you use the metric system because you take your weight in kilograms and divide that by the square of your height in meters, the World Health Organization reports. In the case of the example given earlier, this would be 99.79 kg divided by the square of 1.82 meters or 3.34, and you get a BMI of 29.83.
What Your Body Mass Index Means
A BMI that ranging between 18.5 to 24.99 is considered normal, the World Health Organization reports. You are considered pre-obese if your BMI is from 25 to 29.99. If it is from 30 to 34.99, you are classified as Obese Class I. A BMI of 35 to 39 places you in Obese Class II and 40 or more puts you in Obese Class III. On the opposite end of the scale, a BMI of 17 to 18.49 classifies you as Mildly Thin, while one of 16 to 16.99 makes you Moderately Thin. Anything less than 16 is considered Severely Thin.
Risks of Obesity
Note that not everyone with a BMI greater than 25 is obese because it is not a direct measure of body fat, the Centers for Disease Control and Prevention reports. Muscular athletes tend to have higher BMIs because muscle is heavier than fat, but most people with a BMI of 30 or more do tend to have an increased amount of fat. People who are obese are at a greater risk for hypertension, type 2 diabetes, coronary heart disease, stroke, gallbladder disease, osteoarthritis, sleep apnea and other respiratory problems.
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