BMI Calculator
Body Mass Index, ideal weight, body fat, calorie needs and health-risk assessment with metric or imperial units.
Body Measurements (optional - improves body fat estimate)
Enter your measurements
and press Calculate
About this calculator
WHO BMI Classification
| Category | BMI (kg/m²) | Risk |
|---|---|---|
| Severe Thinness | < 16.0 | Very High |
| Moderate Thinness | 16.0 - 16.9 | High |
| Mild Thinness | 17.0 - 18.4 | Moderate |
| Normal | 18.5 - 24.9 | Average |
| Overweight | 25.0 - 29.9 | Increased |
| Obese Class I | 30.0 - 34.9 | High |
| Obese Class II | 35.0 - 39.9 | Very High |
| Obese Class III | ≥ 40.0 | Extremely High |
Formulas Used
- BMI
- weight(kg) / height(m)²
- BMR (Mifflin-St Jeor)
- Male: 10W + 6.25H − 5A + 5
Female: 10W + 6.25H − 5A − 161 - Body Fat (Deurenberg)
- 1.20 × BMI + 0.23 × Age − 10.8 × sex − 5.4
- Body Fat (U.S. Navy)
- Men: 495 / (1.0324 − 0.19077 × log(W−N) + 0.15456 × log(H)) − 450
Women: 495 / (1.29579 − 0.35004 × log(W+H−N) + 0.22100 × log(H)) − 450 - BSA (Mosteller)
- √(Height(cm) × Weight(kg) / 3600)
- Ponderal Index
- weight(kg) / height(m)³
BMI is a screening tool only. It does not diagnose body fatness or health. Consult a qualified healthcare professional for medical advice.
How to use
- Choose metric (kg, cm) or imperial (lb, in) units.
- Enter your height and weight.
- Optionally add age, sex, activity level and body measurements for richer metrics.
- Press Calculate. The BMI value, category and full breakdown appear instantly.
- Compare your value to the WHO scale and review the healthy weight range.
Frequently asked questions
What is BMI exactly?
Body Mass Index, calculated as weight (kg) / height (m)2. It is a population-level screen, not a body-composition measurement.
How accurate is BMI?
BMI works reasonably well as a screen for groups but can mislabel muscular individuals as overweight and very lean individuals as healthy. Pair it with waist circumference or a body-fat measurement for a fuller picture.
Why are the WHO ranges different from some local guidelines?
Some health authorities use slightly different cut-offs based on local population data, particularly for South and East Asian populations where health risks rise at lower BMIs.
Should children use this calculator?
No. For children and teens, BMI must be interpreted against age and sex percentile charts rather than the adult WHO ranges. Use a paediatric-specific tool.
What BMI measures, and the categories behind the number
BMI is weight in kilograms divided by height in metres squared. At 178 cm and 82 kg: 82 / 1.78^2 = 25.9. The WHO bands... under 18.5 underweight, 18.5-24.9 normal, 25-29.9 overweight, 30+ obese... were derived from population mortality statistics, and at population scale BMI correlates well with metabolic risk. It costs nothing to compute, which is why it remains medicine's universal first-pass screen a full two centuries after Adolphe Quetelet devised it.
Where the formula breaks down
- It cannot see composition: a muscular 90 kg athlete and a sedentary 90 kg office worker at the same height share a BMI and almost nothing else. Rugby players routinely screen as "obese".
- It ignores fat location, yet visceral (abdominal) fat drives metabolic risk far more than fat on hips and thighs.
- Healthy-range cutoffs shift with ethnicity... several Asian populations face elevated diabetes risk from BMI 23... and the formula is not designed for children, for whom age-specific percentile charts apply.
A better five-second check to pair with it
Waist-to-height ratio fixes the biggest blind spot: keep waist circumference under half your height (under 89 cm at 178 cm tall). Someone with a "normal" BMI but a high ratio carries the risk BMI missed; an athlete flagged "overweight" with a low ratio almost certainly is not at risk. Use BMI as a trend line for your own body over time rather than a verdict, and let a physician interpret either number before it drives any decision.
Advertisement