Body Mass Index (BMI)
Body Mass Index (BMI)
The Body Mass Index (BMI), pronounced /ˈbɒdi mæs ˈɪndɛks/, is a value derived from the mass (weight) and height of an individual. The BMI is defined as the individual's body mass divided by the square of their height. It is an attempt to quantify the amount of tissue mass (muscle, fat, and bone) in an individual, and then categorize that person as underweight, normal weight, overweight, or obese based on that value.
Etymology
The term "Body Mass Index" was first coined by the Belgian scientist Adolphe Quetelet in the 19th century during his development of "social physics". The term "Body Mass Index" (BMI) was later popularized in the paper written by Ancel Keys in the Journal of Chronic Diseases in 1972.
Calculation
The BMI is universally expressed in kg/m², resulting from mass in kilograms and height in meters. If pounds and inches are used, a conversion factor of 703 (kg/m²)/(lb/in²) must be applied. The formula is:
- BMI = weight(kg) / (height(m))^2
Categories
The World Health Organization (WHO) has defined the following categories based on BMI values:
- Underweight: a BMI less than 18.5
- Normal weight: a BMI of 18.5–24.9
- Overweight: a BMI of 25–29.9
- Obesity: a BMI of 30 or higher
Limitations
While the BMI can give a general idea of whether a person has a healthy body weight, it does not measure body fat directly. It also does not account for muscle mass, bone density, overall body composition, and racial and sex differences.
Related Terms
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