The body mass index (BMI), or Quetelet index, is a statistical measurement which compares a person's weight and height. Though it does not actually measure the percentage of body fat, it is a useful tool to estimate a healthy body weight based on how tall a person is. Due to its ease of measurement and calculation, it is the most widely used diagnostic tool to identify weight problem within a population including: underweight, overweight and obesity. It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing "social physics". Body mass index is defined as the individual's body weight divided by the square of his height.

• BMI < 16.5 = severely underweight
• BMI 16.5 – 18.5 = underweight
• BMI 18.5 – 25 = normal
• BMI 25 – 30 = overweight
• BMI > 30 = obese

Keep in mind that it is a statistical approximation and does not factor in body type or build. An athlete with higher bone density and muscle mass may be considered overweight or even obese when in actuality they have very low body fat.

More information about calculating BMI -