BMI Calculator
Enter your weight and height in metric or imperial units. You will see your body mass index, the WHO adult category it falls in, and the weight range that corresponds to a BMI of 18.5 to 24.9 at your height.
Enter your numbers to see the result.
How BMI is calculated
Body mass index compares your weight to your height. In metric units it is weight in kilograms divided by height in metres squared. In imperial units it is 703 times weight in pounds divided by height in inches squared. A person who is 70 kg and 170 cm tall has a BMI of 70 ÷ (1.70 × 1.70), which is 24.2.
BMI categories for adults
| BMI | WHO category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity |
What BMI cannot tell you
BMI is a screening number, not a diagnosis. It cannot tell muscle from fat, so a strength athlete can land in the overweight range while carrying very little body fat. It also ignores where fat is stored, and the standard cut-offs can under- or over-estimate risk for some ethnic groups. Waist measurement and blood tests tell you more about health than BMI alone.
This calculator is for adults aged 20 and over. Children and teenagers are assessed using age and sex percentile charts, so please ask a paediatrician instead of using these cut-offs.
Next steps
If your result is outside the normal range, treat it as a reason to talk to a doctor or dietitian, not as a verdict. To estimate how much energy your body uses each day, try the calorie calculator.
This tool is for general information and does not replace medical advice.
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What BMI is
Body mass index (BMI) compares your weight with your height. It is used as a quick screening measure for adults, to flag weights that may be worth discussing with a doctor. It is not a diagnosis, and it does not measure body fat directly. This BMI calculator works in metric (kg and cm) or imperial units (lb and inches) and also shows the weight range that counts as healthy for your height.
The formula
BMI = weight (kg) ÷ height (m)²
BMI = 703 × weight (lb) ÷ height (in)²
For someone who weighs 70 kg and is 175 cm (1.75 m) tall, BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9.
Adult BMI ranges
| BMI | Category (World Health Organization) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity |
How to use your result
Treat BMI as one signal among several. Waist measurement, blood pressure, blood sugar, activity level and family history all say more about health than a single ratio. If you want to track progress, look at how your BMI changes over months rather than days, since daily weight moves with water, food and exercise. A sudden, unexplained change in weight is worth mentioning to a doctor whatever your BMI is.
Limits of BMI
BMI cannot tell muscle from fat, so very muscular people can score as overweight. It does not show where fat is stored, and it does not account for age, sex or ethnicity. Some health bodies use lower cut-off points for people of Asian descent, because health risks can rise at lower BMI values. This calculator is for adults only: for children and teenagers, BMI is read against growth charts for their age. If your result is outside the healthy range, or you are concerned about your weight, speak to a doctor or dietitian.
Frequently asked questions
What is a healthy BMI range?
For most adults, the WHO defines a normal BMI as 18.5 to 24.9. Individual health depends on many other factors, so use the number as a starting point only.
Is BMI accurate for athletes?
Not always. BMI cannot separate muscle mass from fat mass, so muscular people may be classed as overweight even with low body fat.
Can I use BMI for children?
No. Children and teens use age and sex specific percentile charts. This calculator is designed for adults only.
How do I enter imperial height?
Enter your total height in inches. For 5 feet 7 inches, multiply 5 by 12 and add 7 to get 67.