Body mass index to assess body weight

The BMI is a measure of general adiposity. It is calculated using the following formula:

Obesity is classified according to BMI (see Classification of weight according to body mass index). BMI should be interpreted with caution in groups where muscle or fat mass varies significantly (eg very muscular people, older people).

Table 1. Classification of weight according to body mass index
Classification	BMI (kg/m²) [NB1]	Risk of obesity-related comorbidities
underweight	less than 18.5	low (but the risk of other clinical problems is increased)
healthy	18.5 to 24.9	average
overweight	25 to 29.9	increased
obese	30 or more	greatly increased, particularly in association with central fat deposition
class I	30 to 34.9	high
class II	35 to 39.9	very high
class III	40 or more	extremely high
Note: BMI = body mass index NB1: These figures have been determined from population studies. They are based on mortality data for Caucasians and may not be appropriate for other population groups. Lower BMI cut-offs may be considered in Asian populations, including South Asian, Chinese and Japanese people (who may have a higher proportion of body fat), and Aboriginal Australians (who have a high limb-to-trunk ratio). Higher BMI cut-offs may be considered in Pacific peoples, including Māori and Torres Strait Islander peoples (who generally have a higher proportion of lean body mass)World Health Organization (WHO), 2011.