How is BMI calculated and interpreted in adults?
Calculation of BMI
BMI is calculated the same way for both adults and children. The calculation is based on the following formulas:
| Measurement Units |
Formula and Calculation |
| Kilograms and meters (or centimeters) |
Formula: weight (kg) / [height (m)]2
With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters.
Example: Weight = 68 kg, Height = 165 cm (1.65 m)
Calculation: 68 ÷ (1.65)2 = 24.98 |
| Pounds and inches |
Formula: weight (lb) / [height (in)]2 x 703
Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.
Example: Weight = 150 lbs, Height = 5'5" (65")
Calculation: [150 ÷ (65)2] x 703 = 24.96 |
Interpretation of BMI for adults
For adults 20 years old and older, BMI is interpreted using standard weight status categories that are the same for all ages and for both men and women. For children and teens, on the other hand, the interpretation of BMI is both age- and sex-specific. For more information about interpretation for children and teens, visit Child and Teen BMI Calculator.
The standard weight status categories associated with BMI ranges for adults are shown in the following table.
BMI |
Weight Status |
| Below 18.5 |
Underweight |
| 18.5 – 24.9 |
Normal |
| 25.0 – 29.9 |
Overweight |
| 30.0 and Above |
Obese |
For example, here are the weight ranges, the corresponding BMI ranges, and the weight status categories for a sample height.
| Height |
Weight Range |
BMI |
Weight Status |
| 5' 9" |
124 lbs or less |
Below 18.5 |
Underweight |
| 125 lbs to 168 lbs |
18.5 to 24.9 |
Normal |
| 169 lbs to 202 lbs |
25.0 to 29.9 |
Overweight |
| 203 lbs or more |
30 or higher |
Obese |
How reliable is BMI as an indicator of body fatness?
The correlation between the BMI number and body fatness is fairly strong; however the correlation varies by sex, race, and age. These variations include the following examples: 3, 4
- At the same BMI, women tend to have more body fat than men.
- At the same BMI, older people, on average, tend to have more body fat than younger adults.
- Highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness.
It is also important to remember that BMI is only one factor related to risk for disease. 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).
Body Mass Index Table for Adults
References
1Mei Z, Grummer-Strawn LM, Pietrobelli A, Goulding A, Goran MI, Dietz WH. Validity of body mass index compared with other body-composition screening indexes for the assessment of body fatness in children and adolescents. American Journal of Clinical Nutrition 2002;7597–985.
2Garrow JS and Webster J. Quetelet's index (W/H2) as a measure of fatness. International Journal of Obesity 1985;9:147–153.
3Prentice AM and Jebb SA. Beyond Body Mass Index. Obesity Reviews. 2001 August; 2(3): 141–7.
4Gallagher D, et al. How useful is BMI for comparison of body fatness across age, sex and ethnic groups? American Journal of Epidemiology 1996;143:228–239.
5World Health Organization. Physical status: The use and interpretation of anthropometry. Geneva, Switzerland: World Health Organization 1995. WHO Technical Report Series.
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