Adult BMI Calculator
Calculate Body Mass Index (BMI) for adults aged 18 and over from height and weight.
For adults aged 18 and over. This calculator provides general information and is not a diagnosis or medical advice.
Your BMI result
Your BMI result will appear here.
Category:
Healthy BMI range for adults: 18.5 to 24.9
BMI is a screening measure. It does not diagnose a health condition and does not directly measure body fat.
Adult BMI ranges
- UnderweightBelow 18.5Your result
- Healthy weight18.5 to 24.9Your result
- Overweight25.0 to 29.9Your result
- Obesity30.0 and aboveYour result
How we calculated this
BMI is calculated by dividing weight in kilograms by height in metres, squared.
Adult BMI categories
These are adult BMI screening ranges: the thresholds follow the World Health Organization's global classification, and the category names below (including "healthy weight") use the same plain-English wording the NHS uses for the same ranges. Not a diagnosis, and not adjusted for muscle mass, body composition or ethnicity.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity |
Limitations
BMI is not suitable for assessing weight during pregnancy. It is not designed for people under 18, and is less informative for anyone with a diagnosed or suspected eating disorder, or a condition that affects height.
BMI is a screening measure based only on weight and height. It does not directly measure body fat, muscle mass, fat distribution, or overall health, and does not distinguish between muscle and body fat, so it may be less informative for people with high muscularity.
Xiliro uses the standard adult BMI ranges shown above and does not adjust the category according to ethnic background. NHS guidance notes that health risks can occur at lower BMI values for some ethnic groups. For any concerns about your weight or health, speak with a qualified healthcare professional.
Privacy
Your height and weight stay in your browser. They are never sent anywhere.
Sources
BMI classification source: World Health Organization. Adult scope, pregnancy and body-composition guidance reviewed against the NHS.
Health information reviewed: 17 September 2026.
Related information
See Editorial & Calculation Standards for how this and other Xiliro calculators are sourced and tested, and the Disclaimer for the full limitations of every health, financial and maths tool on the site.
What this result means
The category shown is a screening label based only on the WHO adult BMI thresholds — see the categories and limitations below for what it does not tell you.