BMI (Body Mass Index) is a person's weight calculated using their height. It can be used to define if a subject is over or underweight and whether their weight is in healthy proportion to their height. The calculation works out to a person's body weight divided by the square of their height, and can be expressed using the following formula:

BMI = weight (kg)

Height x height (m x m)

For example, if you stood at 6 feet, and weighed 200 pounds, your BMI would be calculated at 27.1. Conversely, if you were 5 feet 5 inches and weighed 100 pounds, your BMI would be 16.6, making you underweight according to the scale. The index at its virtual lowest is 15, which would be at near starvation level, while 40 is considered to be dangerously, or morbidly obese. A BMI of less than 18.5 is generally considered to be underweight, while 25 and above can be seen as being overweight. Many sites will also offer a calculating program from working out your BMI.

BMI = weight (kg)

Height x height (m x m)

For example, if you stood at 6 feet, and weighed 200 pounds, your BMI would be calculated at 27.1. Conversely, if you were 5 feet 5 inches and weighed 100 pounds, your BMI would be 16.6, making you underweight according to the scale. The index at its virtual lowest is 15, which would be at near starvation level, while 40 is considered to be dangerously, or morbidly obese. A BMI of less than 18.5 is generally considered to be underweight, while 25 and above can be seen as being overweight. Many sites will also offer a calculating program from working out your BMI.