BMI Calculator
Your body mass index, what the number means, and the weight range that sits in the healthy band for your height.
Result
What this calculator does
Body mass index is a single number that compares your weight to your height. It was designed in the nineteenth century to describe populations, and it is still the quickest way for a clinician to decide whether weight is worth a conversation. It takes two measurements and no equipment beyond a scale and a tape.
What it cannot do is tell muscle from fat, or account for where that weight sits on your frame. A rugby player and a sedentary person of the same height and weight get an identical BMI and very different health profiles. Treat the number as one input among several — waist measurement, blood pressure, activity level, family history — rather than a verdict.
How to use it
- Choose metric or imperial. Your choice changes the fields below straight away.
- Enter your weight and height. Measure height without shoes, standing straight against a wall.
- Read your BMI and the coloured band showing which category it falls in.
- Check the healthy weight range for your height — often more useful than the index itself, because it is expressed in kilos or pounds you can act on.
The formula
Metric BMI = weight (kg) ÷ height (m)²
Imperial BMI = 703 × weight (lb) ÷ height (in)²
Categories (adults, WHO)
under 18.5 Underweight
18.5 – 24.9 Healthy weight
25.0 – 29.9 Overweight
30.0 and up Obese
The 703 in the imperial formula is just the metric conversion folded into one constant. Both routes give the same answer.
Worked examples
| Scenario | What you enter | Result |
|---|---|---|
| 72 kg, 175 cm | Metric | BMI 23.5 — healthy weight |
| 159 lb, 5 ft 9 in | Imperial | BMI 23.5 — the same person |
| 95 kg, 180 cm | Metric | BMI 29.3 — overweight |
| 52 kg, 168 cm | Metric | BMI 18.4 — just under the healthy band |
| Healthy range at 175 cm | — | 56.7 kg to 76.3 kg |
Frequently asked questions
For most adults the World Health Organization puts the healthy band at 18.5 to 24.9. Below that is classed as underweight, 25 to 29.9 as overweight, and 30 or above as obese. These cut-offs describe statistical risk across large populations. An individual sitting slightly outside the band is not automatically unhealthy, and one sitting inside it is not automatically well.
No, and this is its best-known weakness. Muscle is denser than fat, so a well-trained person can easily land in the overweight or obese range with very low body fat. If you lift seriously or play a contact sport, BMI will overstate your risk. Body-fat percentage, waist-to-height ratio, or simply how your clothes fit are more informative.
Not in the adult form. Children's body composition changes constantly as they grow, so paediatric BMI is read against age-and-sex percentile charts rather than fixed cut-offs. A BMI of 19 might be high for a six-year-old and low for a sixteen-year-old. Use the growth charts your paediatrician uses instead of this calculator.
There is good evidence that they should. Several health bodies recommend lower thresholds for people of South Asian, Chinese and other Asian descent, where cardiometabolic risk rises at a lower BMI — often using 23 rather than 25 as the overweight cut-off. This calculator shows the standard WHO bands; if that guidance applies to you, read your number against the lower thresholds.
It is the weight span that puts you between BMI 18.5 and 24.9 at your height. Many people find it more useful than the index, because it is a number you can act on. At 175 cm, for instance, the range runs from about 56.7 kg to 76.3 kg — a nineteen-kilo window, which shows how broad “healthy” really is.
For predicting metabolic risk, waist circumference and waist-to-height ratio generally do better, because they capture where fat sits rather than how much there is. Abdominal fat carries more risk than the same weight on hips and thighs. A useful rule of thumb: keep your waist under half your height. BMI and waist together tell you more than either alone.
No. This is an information tool, not medical advice, and it does not know your blood pressure, blood sugar, medication, pregnancy status or family history. If your result concerns you, or if you are planning a significant change to how you eat or train, speak to a doctor or a registered dietitian who can see the whole picture.
No. The calculation happens in your browser and nothing is transmitted. Health information is particularly sensitive, so the only thing kept is a short summary in your local history if you leave the page open long enough for it to save — and you can clear that with one tap from the History dialog or the privacy page.
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