How it's calculated
Body mass index (BMI) compares your weight with your height. The calculator uses the formula CDC publishes and puts the result into CDC's adult weight categories, which apply to adults 20 and older "regardless of age, sex, or race."CDC
It also turns the healthy-weight BMI range back into pounds or kilograms for your height, so you can see the weight range that CDC's "healthy weight" category covers.
This is an estimate for general information, not medical advice.
The formula
CDC gives the formula in both unit systems:CDC
- Metric: BMI = weight (kg) ÷ [height (m)]²
- US customary: BMI = weight (lb) ÷ [height (in)]² × 703
The result is rounded to one decimal place, the way CDC reports BMI, and that rounded value is placed in a category:
| CDC adult category | BMI |
|---|---|
| Underweight | less than 18.5 |
| Healthy weight | 18.5 to less than 25 |
| Overweight | 25 to less than 30 |
| Obesity | 30 or greater |
| Class 1 obesity | 30 to less than 35 |
| Class 2 obesity | 35 to less than 40 |
| Class 3 (severe) obesity | 40 or greater |
The healthy-weight range for your height is 18.5 × height² up to (not including) 25 × height², converted back to your units.
Worked example
CDC's own example is an adult 5 feet 8 inches tall who weighs 200 pounds.CDC That is 200 ÷ 68² × 703, a BMI of 30.4, which falls in the Obesity (class 1 obesity) category. At that height, the healthy-weight range runs from 122 lb to under 164 lb.
Your BMI: 23.5 HEALTHY WEIGHT
Assumptions and limitations
- A screening measure, not a diagnosis. CDC notes that BMI does not directly measure body fat, does not distinguish fat from muscle and bone, and does not show what type of fat you have or where you carry it.CDC A very muscular person can have a high BMI without excess fat.
- Adults only. Children and teens are still growing, so CDC compares their BMI with others of the same age and sex as a percentile. For ages 2 through 19, use the CDC Child and Teen BMI Calculator. This calculator shows the number but no category under 20.
- The 703 factor is rounded. US and metric results can differ in the second decimal place, which almost never changes the category.
- One number among many. A health care provider looks at BMI alongside other measures and your history. For another view of body composition, try the body fat calculator; for weight targets based on older formulas, see the ideal weight calculator.
For how BMI, calorie needs and macros fit together, read our guide to BMI, calories and macros.