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Body Mass Index (BMI)

According to the World Health Organization (WHO), the body mass index (BMI) is a tool measuring overweight and obesity. Taking weight and height into account, it represents different levels of health risks.

BMI (kg/m2) is calculated by dividing a person’s weight in kilograms by height in meter squared. BMI cut-points of 25 and 30 are used to classify adults as overweight or obese.

Body Mass Index (BMI) Calculator

Height cmHeight ft  in
Weight KgWeight lb


  • Healthy Weight (BMI >18.5)
  • Overweight (BMI >25)
  • Obese Class I (BMI >30) (BMI >30)
  • Obese Class II (BMI >30) (BMI >35)
  • Obese Class III (BMI >30) (BMI >40)(severe, or morbid obesity)
Classification based on the body mass index

(Reference: International Obesity Task Force (IOTF))

Category BMI (kg/m2)* Risks of co-morbidities
Underweight <18.5 Low (but higher risks for other clinical problems including death)
Normal weight 18.5-24.9 Low
Overweight 25.0-29.9 Some risks
Obese >30.0  
Class I 30.0-34.9 High
Class II 35.0-39.9 Very high
Severe Obesity    
Class III >40.0 Extreme

*Note: These values are age and gender independent and reflect comparable levels of adiposity for different populations.

**Note: Calculating BMI and body fat distribution (waist circumference or abdomen-hip circumference ratio) is essential to evaluate the risk of comorbidities of obesity. An insufficient BMI (< 18.5kg/m2) represents a higher risk of developing other clinical problems.

Waist Circumference Measurement

Waist measurement (abdomen circumference) is an adiposity marker complimentary to BMI. It allows, using a measuring tape, to identify excess fat at the abdomen level. A waist over 88cm for women and 102 for men indicates abdominal obesity. Abdominal obesity is associated with an increased risk of diabetes, hypertension, hypertriglyceridemia and vascular disease.

Desirable Increased Risk High-Risk
Women Men Women Men Women Men
<80cm <94cm >80cm >94cm >88cm >102cm
<32" <37" >32" >37" >35" >40"

For more information on the risks of intra-abdominal obesity, please see the Abdominal Obesity section

Other methods of estimating body fat and body fat distribution include measurements of skinfold thickness, calculation of waist-to-hip circumference ratios, and techniques such as ultrasound, computed tomography, and magnetic resonance imaging (MRI). BMI is just one indicator of potential health risks associated with being overweight or obese. For assessing someone’s likelihood of developing overweight- or obesity-related diseases, the National Heart, Lung, and Blood Institute guidelines recommend looking at two other predictors:

  • The individual’s waist circumference (because abdominal fat is a predictor of risk for obesity-related diseases).
  • Other risk factors the individual has for diseases and conditions associated with obesity (for example, high blood pressure or physical inactivity).

Childhood Obesity
See the related section

For more information about the assessment of health risk for developing overweight- and obesity-related diseases, visit the following Web pages from the National Heart, Lung, and Blood Institute:

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