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BMI Calculator
Calculate your Body Mass Index in metric or imperial units and see your BMI category.
Runs entirely in your browser — nothing you type is uploaded.
How to use the BMI Calculator
- Choose your units: Metric (centimetres and kilograms) or Imperial (feet/inches and pounds).
- Enter your height and weight.
- Press Calculate BMI (or the Enter key). Your BMI and category appear instantly, with the formula and the values you entered.
- Use Reset to clear the fields, or Copy result to copy your BMI.
What BMI means
Body Mass Index (BMI) is a simple number that compares your weight to your height. It is widely used as a quick screening measure to place adults into broad weight categories — underweight, normal weight, overweight or obesity — and to get a rough sense of whether a person’s weight may pose a health risk.
How to calculate BMI
BMI uses one of two equivalent formulas depending on your units:
- Metric
BMI = weight (kg) ÷ height (m)² - Imperial
BMI = 703 × weight (lb) ÷ height (in)²
For example, someone who is 170 cm tall and weighs 65 kg has a BMI of 65 ÷ (1.70 × 1.70) = 22.5, which falls in the normal-weight range.
Metric and Imperial
Metric mode takes height in centimetres and weight in kilograms. Imperial mode takes height in feet and inches and weight in pounds; the calculator converts feet and inches into total inches before applying the imperial formula. Both modes produce the same BMI for the same person — they are just two ways of entering the measurements.
BMI categories (adults)
- Underweight Below 18.5
- Normal weight 18.5 – 24.9
- Overweight 25.0 – 29.9
- Obesity 30.0 and above
Important limitations
BMI is a general screening tool, not a diagnosis, and it has real limits. It does not measure body fat directly and cannot distinguish muscle from fat, so it can over- or under-estimate health risk for very muscular people, athletes, older adults, pregnant people and growing children. It also does not account for where fat is stored or for differences between populations. Use BMI as one rough indicator only, and talk to a qualified healthcare professional for advice about your own health.
Is it private?
Yes. The BMI Calculator runs entirely in your web browser using JavaScript. The height and weight you enter are never sent to a server, never stored, and never shared. There is no sign-up and no tracking.
Frequently Asked Questions
Is the BMI Calculator free?
Yes. It is completely free to use, with no account, sign-up or limits.
How is BMI calculated?
In metric units, BMI = weight in kilograms ÷ (height in metres)². In imperial units, BMI = 703 × weight in pounds ÷ (height in inches)². Both formulas give the same BMI value.
What do the BMI categories mean?
A BMI below 18.5 is classed as underweight, 18.5–24.9 as normal weight, 25.0–29.9 as overweight, and 30.0 or above as obesity. These are the standard adult categories used by health organisations.
Is BMI accurate for everyone?
BMI is a useful general screening tool but it does not measure body fat directly and cannot tell muscle from fat. It can be misleading for very muscular people, athletes, pregnant people, older adults and children, and it is not a diagnosis. For personal health advice, speak to a qualified healthcare professional.
Is my height and weight data stored?
No. All calculations run locally in your browser — the values you enter are never uploaded, saved or shared.
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