BMI, or Body Mass Index, is a measure of a person's body fat, based on a simple calculation of body weight in kilograms, divided by the square of the individual's height in meters. It is used by health professionals around the world to determine whether a person is overweight or clinically obese. A person with a BMI equal to or over 25 is considered overweight, while an index of 30 or more is considered obese. At the opposite end of the scale, a BMI of less than 18.5 is an indication that a person ...