Calculating Your BMI

What's Body Mass Index (BMI)?

Body Mass Index (BMI) is a measure that uses your weight and your height to determine if you are underweight, normal, overweight or obese. Some of the calculators takes into account your gender and your age in order to get a more accurate estimate of how healthy you are. This is especially important for teens because BMI age- and sex-specific percentiles are used for two reasons: The amount of body fat changes with age and differs between girls and boys. The calcuation gauges body fat in order to figure out your health. Too much body fat can lead to some serious diseases, so it is important to keep it in check.

Body Mass Index (BMI) Scale

Every scale is different, so make sure to find a credible one to use. BMI is defined as the individual's body weight divided by the square of their height. There are three mathmatical formulas used that all generate similar answers. One you complete the formula you are given a number which represents your BMI.

Common definitions for each category:

Starvation: less than 15.0
Anorexic: less than 17.5
Underweight: less than 18.5
Ideal: from 18.5 to 25
Overweight: from 25 to 30
Obese: from 30 to 40
Morbidly Obese: over 40

Where BMI Falls Short

BMI should not be the only factor taken into consideration when determining your health. A more muscular teen may have a higher weight and BMI but not have too much body fat. Also, a smaller teen could have an ideal BMI, but might have less muscle and too much body fat. Because of these and other considerations, it's a good idea to talk to your doctor if you have questions about whether you are at your ideal weight.