What Your BMI Tells You
Body mass index, or BMI, is a simple number worked out from your height and weight. Doctors, insurers and health surveys use it as a quick first check of whether someone's weight is in a range that is generally linked with good health. It takes seconds to calculate and needs no equipment beyond a measuring tape and a scale.
Enter your height and weight above, in centimetres and kilograms or in feet, inches and pounds, and your BMI appears instantly. You will also see which category it falls into, where it sits on a colour scale, and the weight range considered healthy for your height. Nothing you type is sent anywhere: the calculation happens in your own browser.
How to Use the BMI Calculator
- Choose Metric or Imperial units. Switching converts any numbers you have already entered.
- Enter your height and weight. Your result updates as you type.
- Add your age if you like. It doesn't change the number, but it lets the calculator remind you when adult categories don't apply.
- Pick the International (WHO) or Asian / Indian scale to see the matching categories.
- Use Copy result to save a short summary for your notes or a doctor's visit.
How BMI Is Calculated
The formula is your weight in kilograms divided by your height in metres, squared. For someone who is 1.70 metres tall and weighs 68 kilograms, that is 68 ÷ (1.70 × 1.70), which comes to 23.5. When you use feet and pounds, the calculator converts them to metric first, so the result is exactly the same either way.
Below the main number you will also find BMI Prime, which is your BMI divided by the upper limit of the healthy range. A value of 1.00 means you are right at that limit, values below 1.00 are under it, and values above are over it. Some people find this easier to read than the raw number.
BMI Categories for Adults
The World Health Organization groups adult BMI like this:
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 and above: obesity, split into class I (30 to 34.9), class II (35 to 39.9) and class III (40 and above)
These ranges apply to adults aged 18 and over, whatever their sex. The table under the calculator highlights the row that matches your result.
Why There Is a Separate Asian Scale
Research has found that people of South Asian, East Asian and Southeast Asian heritage tend to face higher risks of type 2 diabetes and heart disease at lower BMI levels than people of European heritage. Body fat percentage and where fat is stored both play a part.
For this reason, the WHO's Asia-Pacific guidance and Indian clinical guidelines use lower cut-offs. On the Asian / Indian scale, a BMI from 18.5 to 22.9 counts as healthy, 23 to 24.9 as overweight, and 25 or above as obesity. If you are of Asian background, including Indian, this scale usually gives a more realistic picture of your risk. Switch between the two scales to see how your category compares.
Your Healthy Weight Range
Because BMI depends on height, every height has a matching weight range that falls inside the healthy band. The calculator shows that range for you and how your current weight compares with it. For a height of 170 centimetres, for example, the healthy range on the WHO scale runs from about 53.5 to 72 kilograms. Treat it as a broad guide rather than a single target. People of the same height can be perfectly healthy at quite different weights.
What BMI Doesn't Measure
BMI is useful because it is quick and consistent, but it is only a rough screening tool. It can't tell muscle from fat, so athletes and people who do a lot of strength training often show a high BMI while being very fit. It says nothing about where fat sits on the body, and fat around the waist carries more health risk than fat elsewhere. It also doesn't suit everyone:
- Children and teens are assessed with growth charts that take age and sex into account, not with adult categories.
- Pregnant people naturally gain weight, so BMI isn't meaningful during pregnancy.
- Older adults often lose muscle, and a slightly higher BMI may be healthier for them.
For a fuller picture, doctors often look at waist size, blood pressure, blood sugar, cholesterol, activity levels and family history alongside BMI. If your result surprises or worries you, a conversation with a doctor is the best next step. They can look at your overall health rather than a single number.