BMI Calculator
Work out your body mass index and weight category in seconds.
About this tool
A BMI calculator works out your body mass index — a single number that relates your weight to your height and places you in a broad weight category. Enter your weight in kilograms and your height in centimetres, and this calculator instantly shows your BMI along with the category it falls into: underweight, normal weight, overweight or obese.
Body mass index is calculated with a simple, transparent formula: BMI = weight in kilograms divided by the square of your height in metres. The World Health Organization bands are below 18.5 for underweight, 18.5 to under 25 for normal weight, 25 to under 30 for overweight and 30 or above for obese. It is a quick screening figure, not a diagnosis — it does not distinguish muscle from fat or account for age, sex or build.
Use BMI as a starting point for tracking changes over time or for a rough health check before a more detailed assessment. Adjust the weight and height to see how your category shifts. Everything is calculated locally in your browser — your weight and height are never uploaded, logged or stored anywhere.
Examples
Input
Weight 70 kg, height 175 cm
Output
BMI 22.9 · Normal weight
Input
Weight 90 kg, height 175 cm
Output
BMI 29.4 · Overweight
Same height but 20 kg heavier pushes the index from normal weight into the overweight band.
Input
Weight 50 kg, height 170 cm
Output
BMI 17.3 · Underweight
Common uses
- Getting a quick health screening figure before a doctor's appointment
- Tracking how your BMI category shifts as you lose or gain weight over time
- Checking whether your weight sits in the normal range for your height
- Comparing your BMI against the standard WHO weight bands
- Setting a weight target by finding the weight that lands you in the normal range
- Doing a rough fitness baseline before starting a new training or diet plan
Frequently asked questions
Is this BMI calculator free?
Yes. It is completely free to use with no sign-up, no limits and no hidden charges.
How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in metres: BMI = kg / m². For example, 70 kg and 1.75 m gives 70 / (1.75 × 1.75) = 22.9.
What is a healthy BMI range?
Under the WHO bands, a BMI below 18.5 is underweight, 18.5 to under 25 is normal weight, 25 to under 30 is overweight, and 30 or above is obese.
Is BMI accurate for everyone?
BMI is a quick screening number, not a diagnosis. It does not separate muscle from fat or adjust for age, sex, ethnicity or build, so very muscular people can read high. Treat it as a starting point, not a verdict.
Is my data private?
Yes. Every calculation runs locally in your browser. Your weight and height are never sent to a server, logged or stored.
Embed this tool
Free to use on your own site. It stays fast and private for your visitors.
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