Free adult BMI calculator
Body mass index, or BMI, compares body weight to height. It is commonly used as a quick screening number for adults because it is simple, fast, and easy to compare over time. It is not a complete picture of health.
BMI does not measure body fat directly and does not know whether weight comes from muscle, bone, fluid, or fat. Use it as a starting point, then consider waist measurement, body composition, activity, medical history, and professional guidance.
BMI formula and categories
Metric BMI equals weight in kilograms divided by height in meters squared. U.S. units are converted to the same scale. Adult categories are typically: underweight below 18.5, normal range from 18.5 to 24.9, overweight from 25 to 29.9, and obesity range at 30 or higher.
| BMI range | Adult category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Normal range |
| 25.0–29.9 | Overweight |
| 30.0+ | Obesity range |