An obese male with a body mass index of 46 kg/m2. Weight 146 kg (322 lbs), height 177 cm (5 ft 10 in)
Body mass index or BMI is a simple and widely used method for estimating body fat mass.BMI was developed in the 19th century by the Belgian statistician and anthropometrist Adolphe Quetelet.BMI is an accurate reflection of body fat percentage in the majority of the adult population. It is less accurate in people such as body builders and pregnant women in whom body composition is affected.
BMI is calculated by dividing the subject's mass by the square of his or her height, typically expressed either in metric or US "Customary" units:
Metric: BMI = kilograms / meters2
US/Customary and imperial: BMI = lb * 703 / in2
Less than 18.5 underweight
18.5–24.9 normal weight
25.0–29.9 is overweight
30.0–34.9 is class I obesity
35.0–39.9 class II obesity
Over 40.0 class III obesity
The most commonly used definitions, established by the WHO in 1997 and published in 2000, provide the values listed in the table at right.
Some modifications to the WHO definitions have been made by particular bodies. The surgical literature breaks down "class III" obesity into further categories.
Any BMI > 40 is severe obesity
A BMI of 40.0–49.9 is morbid obesity
A BMI of >50 is super obese
As Asian populations develop negative health consequences at a lower BMI than caucasions some nations have redefined obesity. The Japanese have defined obesity as any BMI greater than 25 well China uses a BMI of greater than 28.