Body Mass Index (BMI) is a more accurate measurement than weight because it takes into account short people tend to weigh less than tall people. It is not perfect, however.
The BMIs of highly muscular athletes are often in the obese range. Still, it has become more of the standard for definition of morbid obesity than its predecessor, the 1983 Metropolitan Height and Weight tables (click here to view).

BMI is calculated by dividing weight in pounds by height in inches squared then multiplying by 703.

Take a 200 pound individual who is six feet tall (72 inches). His BMI is 200 divided by 5184 (72 x 72) x 703 or 27.1.

The table to the right correlates BMI to weight status. Even though a BMI or 40 or greater constitutes morbid obesity, greater health risks begin with a BMI of 30 or greater as the graph below shows: