BMI Calculator
Find your Body Mass Index (BMI) and weight category in seconds.
How to use the BMI Calculator
- Enter your weight in kilograms.
- Enter your height in centimetres.
- Your BMI and weight category (underweight, normal, overweight, obese) appear instantly.
BMI = weight (kg) ÷ height (m)²
About the BMI Calculator
Body Mass Index is a screening figure that compares your weight to your height. Enter your weight in kilograms and your height in centimetres, and the calculator divides your weight by the square of your height in metres to give a BMI to one decimal place, the category it falls in, and the weight range that would put you in the healthy band for your height.
The standard adult categories are under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, and 30 and above obese. These are the thresholds health services use worldwide as a first, rough indicator — the same reason BMI endures despite its flaws: it needs only two numbers anyone can measure.
Treat the result as a starting point, never a diagnosis. BMI does not measure body fat and cannot tell muscle from fat, so a very muscular person can read as overweight while carrying little fat. It ignores where fat sits on the body, and takes no account of age, sex or ethnicity, all of which shift what a given number means. It is built for adults; children and teenagers are assessed on age- and sex-specific percentiles instead. This is information, not medical advice — discuss anything that concerns you with a doctor. For daily calorie needs see the BMR calculator, or compare against the ideal weight calculator.
Frequently asked questions
What is a healthy BMI?
For adults, a BMI between 18.5 and 24.9 is generally considered the healthy range. Below 18.5 is classed as underweight, 25 to 29.9 as overweight, and 30 or more as obese.
Is BMI accurate for athletes?
Often not. Muscle is denser than fat, so a very muscular person can land in the overweight or obese category while carrying very little fat. If you train seriously, a body-fat measurement tells you far more than BMI does.
Does BMI work for children?
No. Children and teenagers are assessed using age- and sex-specific BMI percentiles, because healthy ranges change as they grow. This calculator uses the adult categories only.
What units does it take?
Kilograms for weight and centimetres for height. If you work in pounds and feet, convert first: one pound is about 0.4536 kg, and one foot is 30.48 cm.
Why does the healthy weight range matter more than the BMI number?
Because a range in kilograms is something you can act on. The calculator shows the weight span that corresponds to a BMI of 18.5 to 24.9 at your height, which is easier to interpret than a single index value. It is still a guide, not a target set by a clinician.
Guides & articles about this tool
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