BMI Calculator
Enter your height and weight to calculate BMI with a category rating (underweight, normal, overweight, obese). Supports metric and imperial units. For informational purposes only.
Updated July 11, 2026
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Your data is never uploaded or stored.
How to use
- 1
Enter your height and weight.
- 2
Click Calculate.
- 3
Review your BMI and weight range.
How it works
WHO adult BMI categories
The World Health Organization classifies adult BMI (ages 20+) into bands. The cutoffs are the same for men and women, but population health risks rise sharply at the extremes.
| Category | BMI (kg/m²) |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese (Class I) | 30.0 – 34.9 |
| Obese (Class II) | 35.0 – 39.9 |
| Obese (Class III) | ≥ 40.0 |
Why BMI is only a screening tool
BMI correlates with body fat at the population level but is a noisy signal for any individual. It cannot distinguish lean mass from fat, so muscular athletes routinely score "overweight," and it underestimates adiposity in older adults who have lost muscle. It also does not capture fat distribution — visceral (abdominal) fat carries higher metabolic risk than subcutaneous fat on the limbs.
For children and teens (under 20), BMI must be plotted on age- and sex-specific percentile charts, not the adult cutoffs. This tool applies the adult standard only.
How this is calculated
- Formula:
- BMI = weight (kg) ÷ height² (m²). In imperial units: BMI = weight (lb) ÷ height² (in²) × 703.
- Applies to:
- WHO international adult standard, ages 20+.
BMI is a population-level screening measure, not a diagnosis of body fatness or health. It does not account for muscle mass, bone density, age, sex, or pregnancy. This tool is for informational purposes only and is not medical advice — consult a licensed healthcare provider for an individual assessment.