Body mass index

Body mass index (BMI)
Chart showing body mass index (BMI) for a range of heights and weights in both metric and imperial. Colours indicate BMI categories defined by the World Health Organization; underweight, normal weight, overweight, moderately obese, severely obese and very severely obese.
SynonymsQuetelet index
MeSHD015992
MedlinePlus007196
LOINC39156-5
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Body mass index (BMI) is a value derived from the mass (weight) and height of a person. The BMI is defined as the body mass divided by the square of the body height, and is expressed in units of kg/m2, resulting from mass in kilograms (kg) and height in metres (m).

The BMI may be determined first by measuring its components by means of a weighing scale and a stadiometer. The multiplication and division may be carried out directly, by hand or using a calculator, or indirectly using a lookup table (or chart).[a] The table displays BMI as a function of mass and height and may show other units of measurement (converted to metric units for the calculation).[b] The table may also show contour lines or colours for different BMI categories.

The BMI is a convenient rule of thumb used to broadly categorize a person as based on tissue mass (muscle, fat, and bone) and height. Major adult BMI classifications are underweight (under 18.5 kg/m2), normal weight (18.5 to 24.9), overweight (25 to 29.9), and obese (30 or more).[1] When used to predict an individual's health, rather than as a statistical measurement for groups, the BMI has limitations that can make it less useful than some of the alternatives, especially when applied to individuals with abdominal obesity, short stature, or high muscle mass.

BMIs under 20 and over 25 have been associated with higher all-cause mortality, with the risk increasing with distance from the 20–25 range.[2]


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  1. ^ Cite error: The named reference World Health Organization 2006 was invoked but never defined (see the help page).
  2. ^ Di Angelantonio E, Bhupathiraju S, Wormser D, Gao P, Kaptoge S, Berrington de Gonzalez A, et al. (August 2016). "Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents". Lancet. 388 (10046): 776–86. doi:10.1016/S0140-6736(16)30175-1. PMC 4995441. PMID 27423262.