How to use the BMI Calculator tool
- Choose your unitsUse centimetres and kilograms, or feet, inches and pounds.
- Enter height and weightYour BMI is calculated instantly as you type.
- Read your resultSee your BMI, its category, where it sits on the scale, and the healthy weight range for your height.
What this BMI calculator gives you
- BMI valueCalculated with the standard formula used by the World Health Organization (WHO).
- CategoryUnderweight, healthy weight, overweight or obesity, based on the WHO adult ranges.
- Visual scaleA color bar shows where your BMI sits between the categories.
- Healthy rangeThe weight range that corresponds to a BMI of 18.5–24.9 for your height.
- Both unit systemsSwitching units converts your numbers automatically.
- PrivateYour measurements never leave your browser.
What is BMI?
Body Mass Index (BMI) is a simple number that relates your weight to your height. It is widely used as a quick screening tool to see whether an adult’s weight falls in a range generally associated with lower or higher health risks. It does not measure body fat directly and is not a diagnosis.
How BMI is calculated
BMI = weight (kg) ÷ height (m)²
For example, a person who is 1.70 m tall and weighs 68 kg has a BMI of 68 ÷ (1.70 × 1.70) = 23.5. In imperial units the formula is weight (lb) ÷ height (in)² × 703, which gives the same result.
BMI categories for adults
| BMI | Category (WHO) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Some health authorities recommend lower cut-off points for people of South Asian, Chinese and some other Asian backgrounds, because health risks can rise at a lower BMI. For example, guidance in India and from NICE in the UK suggests that a BMI of 23 or more may already indicate increased risk for these groups. Ask your doctor which thresholds apply to you.
Limitations of BMI
- Muscle vs fat. Athletes and very muscular people can have a high BMI without excess body fat.
- Body fat distribution. BMI doesn’t show where fat is stored. Waist circumference is often used alongside BMI because fat around the abdomen is linked to higher risk.
- Age and sex. Older adults naturally lose muscle, and body composition differs between men and women at the same BMI.
- Children and teens. For people under 20, BMI must be compared with age- and sex-specific percentile charts. The adult categories above do not apply.
- Pregnancy. BMI is not meaningful during pregnancy.
What should I do with my result?
BMI is a starting point for a conversation, not a verdict. If your result is outside the healthy range, or you have concerns about your weight, talk to a doctor or a registered dietitian. They can consider your overall health, lifestyle, family history and other measurements to give advice that fits you. This calculator provides general information and is not medical advice.