Formulas

Body Mass Index (BMI) - describes relative weight for height. BMI is often used as a predictor of future disease risk. However, one can be overweight and not be obese. 

Divide ones weight (in kilograms) by ones height (in meters) squared to determine ones BMI. 

Weight Ibs x 703

Height^ (inch^)

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Overweight -  refers to an excess amount of weight that includes all tissues: bone, muscle, water, and fat. 

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Obesity refers specifically to body fat. The National Heart, Lung, and Blood Institute (NHLBI) recommends that BMI be used to assess overweight and obesity and not to monitor changes in body weight. According to an expert panel formed in 1998 by the NHLBI, BMI is the key preferred measure to be used in clinical guidelines for the identification, evaluation and treatment of overweight and obesity in adults. 

Since body weight (and not body fat percentage) is solely used in determining BMI, it may not be the best way to assess those who have a larger percentage of muscle (such as bodybuilders) or who have an athletic body type. Because muscle weighs more than fat, those who have well-developed muscles typically appear overweight or obese according to the BMI reference chart. ​

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Underweight                      <18.5

Normal                               18.5 - 24.9

Overweight                          25.0 - 29.9

Obeisity, Class I                    30.0 - 34.9

Obesity, Class II                    35.0 - 39.9

Extreme Obesity, Class III      >40

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