BMI Calculator
Calculate body mass index in metric or imperial units, see which category it falls in, and the healthy weight range for your height.
How to use it
- Switch between metric and imperial with the toggle.
- Your BMI and its category appear on a colour scale.
- The healthy weight range for your height is shown underneath.
Body mass index is weight divided by height squared (kg ÷ m²), a quick screening number used by clinicians and public health bodies worldwide. This calculates it in metric or imperial units, places it on the standard category scale, and shows the weight range that would count as 'healthy' for the height entered.
The standard BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
A worked example
A person 1.75m tall weighing 70kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9 — inside the healthy range. In imperial terms, the same calculation uses BMI = 703 × weight (lb) ÷ height (in)², which is the metric formula rescaled for pounds and inches so the category boundaries come out the same.
What BMI doesn't capture
BMI cannot distinguish muscle mass from fat mass, which is why heavily muscled athletes routinely score as 'overweight' or even 'obese' despite low body fat. It also doesn't account for where fat is distributed, which matters more for health risk than the total amount, and it's less reliable across children, older adults, and pregnancy, where the standard adult categories don't apply the same way. It's a fast first-pass screening number, not a diagnosis.
Questions people ask
Is BMI accurate for everyone?
It is a rough screening tool, not a diagnosis. It does not distinguish muscle from fat, so athletes often read as overweight, and it is less reliable for children, older adults and pregnancy. Treat it as one data point and talk to a clinician for anything that matters.
Last updated 17 August 2026