BMI Calculator
BMI is a quick screening ratio, not a diagnosis. It is calculated here alongside an explanation of where it works and where it does not.
| Height used | — |
| Weight used | — |
| Healthy-range weight at this height | — |
How to use the BMI Calculator
- Choose metric or imperial units.
- Enter your height and weight.
- Press Calculate BMI to see the figure, its category, and the weight range that corresponds to a BMI of 18.5–24.9 at your height.
The formula and the categories
BMI is weight in kilograms divided by height in metres squared. In imperial units the equivalent is (pounds ÷ inches²) × 703 — the constant just converts units, so both give the same number.
| BMI | WHO category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy range |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese (classes I–III) |
What BMI cannot tell you
BMI was devised in the 1830s to describe populations, not to assess individuals. It uses only two numbers, so it cannot distinguish muscle from fat or know where weight is carried. Several groups are systematically misread:
- Muscular people. Athletes frequently score as overweight or obese with low body fat.
- Older adults. Muscle loss can keep BMI unchanged while body composition shifts substantially.
- Different ancestries. Health risks rise at lower BMI thresholds in South and East Asian populations; several countries use adjusted cut-offs.
- Children and teenagers. Adult categories do not apply — paediatric BMI is read against age and sex percentile charts.
- Pregnancy. BMI is not meaningful during pregnancy.
Waist circumference and waist-to-height ratio capture fat distribution, which correlates better with metabolic risk. A useful rule of thumb is keeping your waist under half your height.
Frequently asked questions
Is BMI accurate for me personally?
It is a screening ratio, not a measurement of your body. Two people with the same BMI can have very different body composition and health. Treat it as one rough data point among several.
Why does my BMI differ from a gym machine's reading?
Body composition scales estimate fat percentage by passing a small current through the body — an entirely different measurement. They are also sensitive to hydration and time of day.
Can I use this for a child?
No. Children's BMI must be read against age and sex growth charts, since healthy ranges change throughout development. Ask a paediatrician or use a dedicated paediatric chart.
Is any data stored?
No. The calculation runs in your browser and nothing is transmitted or saved.
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