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An indirect measure of body fat. Identifies possible weight problems for adults, and allows individuals to compare their weight status to that of the general population. BMI = weight(kg)/height(m2).  

Interpretation of BMI in adults

  • Less than 18.5 = Underweight
  • Between 18.5 - 24.9 = Health weight
  • Between 25–29.9 kg/m2 = Overweight 
  • Over 30 kg/m2 = Obese 
  •  Over 40 kg/m2 = Morbidly obese

BMI takes no account of fat distribution or body composition; for example, a highly trained athlete may have a high BMI because of increased muscularity rather than increased body fat. An alternative predictor of risk for obesity-related diseases is waist circumference. 

Black, Asian and other minority ethnic groups are aware that they face an increased risk of chronic health conditions at a lower BMI than the white population (below 25  kg/m2).

BMI Calculator Patient Professional Reference/Medical calculators 

NICE CG189. Obesity: identification, assessment and management; 2014.

NICE PH46. BMI: preventing illhealth and premature death in black, Asian and other minority ethnicities; 2013

Interpretation of BMI in children

Specific age-adjusted and sex-specific charts must be used for children.

About BMI for children and teens US Centers for Disease Control and Prevention (CDC) 

Practice Nurse featured article 

Practical Skills in Primary Care: Part 1 Stephanie Garner 

Practice Nurse Curriculum Module

Routine Tests - Part 1


See Obesity, Waist circumference

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