BMI Calculator (body mass index)
Calculate body mass index from height and weight in metric or imperial units, see the category it falls in, and the healthy weight range for your height.
BMI categories (adults)
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese (class I) |
| 35.0 – 39.9 | Obese (class II) |
| 40.0 and above | Obese (class III) |
Body mass index
BMI compares weight to height with a single number. It was designed in the 19th century to describe populations, and it remains useful as a quick screening figure — but it says nothing about an individual's health on its own.
BMI = weight (kg) / height (m)²
For imperial units the equivalent is 703 × pounds / inches², which this calculator applies when you switch units. The category boundaries above are the standard WHO adult ranges.
What BMI misses
Because it only knows height and weight, BMI can't tell muscle from fat. A muscular athlete often lands in the "overweight" or even "obese" band while carrying very little fat, and someone with low muscle mass can sit in the "healthy" band while carrying a lot. It also ignores where fat is stored — abdominal fat carries more health risk than the same weight elsewhere — and the standard ranges don't apply to children, pregnancy, or older adults, with some evidence that they suit different ethnic groups differently.
Worked example
Someone 1.75 m tall weighing 70 kg has a BMI of 70 / 1.75² = 22.9, inside the healthy band. For that height, the healthy range runs from about 56.7 kg (BMI 18.5) to 76.3 kg (BMI 24.9) — a spread of nearly 20 kg, which is a reminder of how broad the "healthy" category really is.
This is a general-information estimate, not medical advice.Use it as one rough indicator among many, and talk to a doctor about your individual situation. Waist measurement, body composition, and blood markers all tell you more than BMI alone.