calculation of body mass index

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The body mass index is a measure of mass that is practically independent of height. It is a useful tool, particularly when a trend is followed, for monitoring relative nutritional status. However, it is not trully dissociated from height and its accuracy decreases with age as vertebral height diminishes.

This is given by W / (H*H) where W is weight in kilograms H is height in metres Normal values for adults are:

  • Underweight <18.5
  • Normal weight =18.5-24.9
  • Overweight = 25-29.9
  • Obesity = BMI of 30 or greater

Click here for BMI calculator

Note that WHO advice on BMI public health action points for Asian populations (World Health Organization 2004) has been incorporated into NICE guidance (1). NICE have produced guidance that assesses how body mass index (BMI) and waist circumference among adults from Asian groups in the UK links to the risk of a range of noncommunicable diseases:

  • aim was to determine whether lower cut-off points or thresholds should be used for these groups, compared to those used for the white population, as a trigger for lifestyle interventions to prevent conditions such as diabetes, myocardial infarction or stroke
White European populations Asian populations Description
Less than 18.5 kg/m² Less than 18.5 kg/m² underweight
18.5-24.9 kg/m² 18.5-23 kg/m² increasing but acceptable risk
25-29.9 kg/m² 23-27.5 kg/m increased risk
30 kg/m² or higher 27.5 kg/m² or higher high risk



  • NICE (July 2013).Assessing body mass index and waist circumference thresholds for intervening to prevent ill health and premature death among adults from black, Asian and other minority ethnic groups in the UK.

Last reviewed 08/2021