BMI Calculator
Free online BMI calculator. Check your Body Mass Index with metric or imperial units, plus healthy-weight range reference.
<18.5Normal
18.5-24Overweight
24-28Obese
≥28
Normal weight — keep up your good diet and exercise habits.
Healthy weight range: 56.7 - 73.5 kg
BMI Calculator guide
How BMI is calculated, precisely
Metric: BMI = weight (kg) ÷ height (m)². For 70 kg at 1.75 m: 70 ÷ (1.75 × 1.75) = 22.9. Imperial: 703 × pounds ÷ inches². The formula dates to 1832 (Lambert Adolphe Quetelet) and was designed for population statistics — which is both its strength (simple, comparable) and its weakness (it measures total mass, not composition).
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity (classes 1-3) |
Where BMI misleads
Muscle is denser than fat: athletes with 10% body fat can score “overweight”. Elderly people lose muscle, so a “healthy” BMI can mask sarcopenia. Asian populations face elevated health risks at lower BMIs — several countries use 23 as the overweight cutoff instead of 25. And fat distribution matters more than total: waist circumference and waist-to-height ratio (keep waist under half your height) predict cardiometabolic risk better than BMI alone.
Using BMI sensibly
Treat it as a trend indicator, not a verdict: measure under consistent conditions and watch the direction over months. Pair it with waist measurement for a two-number picture that beats either alone. And for any personal health decision — weight targets, diet changes, fitness programs — a clinician who can see the whole picture beats any calculator.