Defining Obesity

Body mass index (BMI) is used to classify someone as underweight, at a healthy weight, overweight, or obese. (A high BMI can indicate high body fatness.)

BMI is calculated from an individual’s height and weight using the following formula:
BMI (kg/m2) = [weight in pounds / (height in inches x height in inches)] x 703

BMI Classifications for Adults:

  • Underweight: BMI < 18.5 kg/m2
  • Healthy weight: BMI 18.5-24.9 kg/m2
  • Overweight: BMI 25.0-29.9 kg/m2
  • Obese: BMI >/= 30 kg/m2

BMI Classifications for Children and Adolescents:

For children and adolescents, BMI is compared to growth charts that show BMIs for different ages and genders.

  • Underweight: BMI-for-age < 5th percentile
  • Healthy weight: BMI-for-age >/= 5th percentile to < 85th percentile
  • Overweight: BMI-for-age >/= 85th percentile to < 95th percentile
  • Obese: BMI-for-age >/= 95th percentile