Definitions – BMI Visualizations

Body Mass Index (BMI) is a person’s weight in kilograms divided by the square of height in meters

BMI in Adults (20+ years)
  • Underweight: < 18.5 BMI
  • Normal weight: 18.5 to < 25.0 BMI
  • Overweight: 25.0 to < 30.0 BMI
  • Obese: ≥ 30
Categories of Obesity in Adults (20+ years)
  • Class 1: 30 to < 35.0 BMI
  • Class 2: 35 to < 40.0 BMI
  • Class 3: ≥ 40.0 BMI
BMI in Children/Adolescents (2-19 years)
  • Underweight: < 5th percentile
  • Normal weight: 5th to < 85th percentile
  • Overweight: 85th to < 95th percentile
  • Obese: ≥ 95th percentile
Pregnant women and people with missing values for either weight or height are excluded.

Hispanic designation to Race/Ethnicity represents Mexican Americans up through 2006. After a sampling redesign in 2007, Hispanic designation includes all Hispanics. More details on survey design changes and analytic note can be found here.

Non-Hispanic Asians are reported separately only from 2011-12. Non-Hispanic Asians were included in the “Other” category in 2009-10.

Data Source and Methods

Data from the National Health and Nutrition Examination Surveys (NHANES) 1999-2016 are used for these visualizations. For smaller sub-populations the estimates are based on four years of data (two cycles merged) for statistical stability. Estimates are age-adjusted to the subpopulations based on the population distribution as of 2000 census. Appropriate sampling weights were used so that the sum of the weights added to the total U.S. population.

NHANES is a cross-sectional survey designed to monitor the health and nutritional status of the civilian noninstitutionalized U.S. population using highly stratified, multistage probability designs. The survey consists of interviews conducted in participants’ homes and standardized health examinations conducted in mobile examination centers (MECs). The anthropometry component methodology has remained consistent over time of NHANES cycles. Weight has been measured to the nearest 0.1 kilogram using a digital weight scale. Waist circumference measurements have been made to the nearest 0.1 centimeter using a tape measure at the uppermost lateral border of the hip crest (ilium) (10). Standing height has been measured with a wall-mounted digital stadiometer.

For more information about the National Health and Nutrition Examination Survey, you may visit the NHANES website at: