What is BMI?
Body mass index (BMI) is a number calculated from your weight and height. In US units, the formula is BMI = 703 × weight (lb) ÷ height (in)². It's widely used as a quick screening tool because it's simple and inexpensive.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 or higher | Obesity |
These categories apply to adults age 20 and older. Children and teens are assessed with age- and sex-specific BMI percentiles, so this calculator isn't designed for them.
Limitations of BMI
- It doesn't measure body fat directly. Muscular people may have a high BMI without excess fat.
- It doesn't show where fat is stored. Abdominal fat carries more health risk, which is why waist size adds useful information.
- It can vary in meaning across groups. The relationship between BMI and health risk differs with age, sex and ethnicity. For example, some people of Asian descent may face higher health risks at lower BMIs.
- It's one data point. Blood pressure, blood sugar, cholesterol, fitness and family history all matter too.
Curious about a weight range for your height? Try the ideal weight calculator.
Important
This calculator provides a general estimate for educational purposes only. It isn't a diagnosis or a personalized medical recommendation. Talk with your doctor or a registered dietitian about your individual needs. See our medical disclaimer.