BMI is the statistical measure of a person's weight scaled according to height. The formula for deriving BMI is body weight divided by the square of the height:
A BMI of less than 15 is classified as starvation, underweight from 15 to 18.5. Normal body weight has BMI of 18.5 - 25, while overweight persons usually have BMI of 25-30. A BMI of 30-40 is considered obesity.