How it’s calculated
Body mass index is weight divided by height squared. US units are converted to metric first (the classic imperial shortcut is 703 × lb ÷ in²).
| BMI | CDC category (adults 20+) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to < 25 | Healthy weight |
| 25 to < 30 | Overweight |
| 30 to < 35 | Obesity, class 1 |
| 35 to < 40 | Obesity, class 2 |
| 40 or more | Obesity, class 3 (severe) |
Example: 160 lb at 68 in: 160 × 0.45359 = 72.57 kg; 68 × 0.0254 = 1.7272 m; BMI = 72.57 ÷ 1.7272² = 24.3, in the healthy weight range.
BMI is a screening tool. It does not distinguish muscle from fat, and the same BMI can mean different health risks for different people. Talk to a healthcare provider about your weight.
Frequently asked questions
Is BMI accurate for athletes?
Not always. Muscle is dense, so muscular people can have a high BMI without excess fat. Waist circumference and other measures help.
Can I use this for children or teens?
No. Under age 20, BMI is interpreted with age- and sex-specific percentiles. Use the CDC child and teen BMI calculator.
What is a healthy BMI?
For adults the CDC healthy weight range is 18.5 to less than 25.
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Sources
- Adult BMI Categories — U.S. Centers for Disease Control and Prevention
- About Body Mass Index (BMI) — U.S. Centers for Disease Control and Prevention
Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.
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