BODY MASS INDEX (BMI)

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.  https://www.nice.org.uk/guidance/cg189

NICE PH46. BMI: preventing illhealth and premature death in black, Asian and other minority ethnicities; 2013 https://www.nice.org.uk/guidance/ph46

Interpretation of BMI in children

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

See Obesity, Waist circumference