BMI Calculator
Work out your body mass index in metric or US units, see where you sit on the scale and find the healthy weight range for your height.
- Healthy weight for your height—
- To reach a healthy BMI—
- BMI Prime (BMI ÷ 25)—
BMI is a screening number, not a diagnosis. It does not tell muscle from fat, and it is not used for children, teens or during pregnancy. Speak to a doctor about your health.
How BMI is calculated
Body mass index compares your weight with your height. The formula is your weight in kilograms divided by your height in metres squared. For example, 70 kg at 1.70 m gives 70 ÷ (1.70 × 1.70) = 24.2.
If you use pounds and inches, the calculator converts them for you. The US formula is 703 × weight in pounds ÷ height in inches squared, and it gives the same answer.
What your BMI means
These are the adult categories used by the World Health Organization:
- Under 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 to 34.9: obese, class 1
- 35 to 39.9: obese, class 2
- 40 and above: obese, class 3
Healthy weight range and BMI Prime
The healthy weight range shows the weights that give a BMI between 18.5 and 24.9 at your height. If you are outside it, the calculator shows roughly how much you would need to gain or lose to reach the edge of the range.
BMI Prime is your BMI divided by 25, the top of the healthy range. A value under 1.00 means you are below the upper limit; 1.20 means you are 20% above it.
Limits of BMI
BMI is a quick screening tool, not a diagnosis. It cannot tell muscle from fat, so athletes may score high, and older adults who have lost muscle may score in range while carrying extra fat. Some health bodies suggest lower cut-offs for people of South Asian, Chinese and other Asian backgrounds. Children, teens and pregnant women need different measures. For advice about your own health, talk to a doctor.
BMI Calculator FAQs
Answers about BMI ranges, accuracy and who it is for.
What is a healthy BMI?+
For most adults, a BMI from 18.5 to 24.9 is classed as a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or more is obese.
Is BMI accurate?+
It is a useful quick check for most adults, but it does not measure body fat directly. Muscular people can have a high BMI without extra fat. Waist size and other checks give a fuller picture.
Can I use this BMI calculator for children?+
No. Children and teens use BMI-for-age percentile charts, because their bodies change as they grow. Ask a doctor or use a child-specific growth chart.
Is BMI different for men and women?+
The formula and adult categories are the same for both. Women usually carry more body fat than men at the same BMI, which is one reason BMI is only a starting point.
Is my data saved?+
No. The calculation runs in your browser. Your height and weight are never sent to our servers.
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