BMI Calculator
Calculate your Body Mass Index in seconds. Get your category, healthy weight range, and a quick reality check on what BMI does (and doesn't) measure.
The math behind BMI
BMI is a screening number that estimates body fat from your height and weight. The formula is dead simple:
For imperial units, we convert to metric first (1 lb = 0.453592 kg, 1 in = 0.0254 m), then run the same formula.
The BMI categories are defined by the World Health Organization:
- Under 18.5 — Underweight
- 18.5 – 24.9 — Normal weight
- 25 – 29.9 — Overweight
- 30+ — Obese
BMI is a screening tool, not a diagnosis. It doesn't measure body fat directly, and it's often wrong for athletes, pregnant people, the elderly, and growing teens. Use it as one data point — not the final word on your health.
Frequently asked questions
BMI (Body Mass Index) is your weight in kilograms divided by the square of your height in meters: BMI = kg / m². It's a quick screening tool — not a diagnosis — used to categorize underweight, normal, overweight, and obese ranges.
For adults, a BMI between 18.5 and 24.9 is generally considered healthy. Below 18.5 is underweight, 25-29.9 is overweight, and 30+ is obese. These ranges are based on WHO guidelines.
No — BMI can overestimate body fat in muscular people because muscle is denser than fat. Athletes often score as 'overweight' despite being lean. Body-fat percentage and waist-to-hip ratio are better measures for them.
Not directly. Children and teens use age-and-sex-specific percentile charts (BMI-for-age), not the adult categories. This calculator is for adults 20 and over.
No. The calculation happens entirely in your browser. Nothing is uploaded, stored, or tracked.
More tools coming for health & fitness.
Calorie calculator, heart-rate zones, training pace, and one-rep max are next.
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