BMI Calculator
BMI is weight in kilograms divided by height in meters squared. A person who is 175 cm tall and weighs 70 kg has a BMI of 22.9, which the WHO classes as normal. For adults, 18.5 to 24.9 is the normal range.
How to use
- Choose Metric (cm, kg) or US units (feet, inches, pounds).
- Enter your height, weight and age. The result updates as you type.
- Read your BMI and its WHO category, plus the weight range that would give a BMI between 18.5 and 24.9 at your height.
How it works
BMI = weight in kg / (height in m)². In pounds and inches the same number is 703 x weight in lb / (height in inches)². A 175 cm, 70 kg adult has 70 / 1.75² = 22.9.
Adult categories follow the World Health Organization: under 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight (pre-obese), 30 to 34.9 obesity class I, 35 to 39.9 class II, and 40 or more class III.
BMI is a screening number, not a diagnosis. It cannot tell muscle from fat, and it does not account for age, sex, ethnicity or where fat is carried. For children and teens (under 18) the adult cut-offs do not apply, because healthy BMI changes with age and sex; they are judged against growth charts (CDC or WHO BMI-for-age percentiles), so this tool shows the number only and no category.
This is general information, not medical advice. Talk to a doctor about your weight and health.
WHO adult BMI categories
| BMI (kg/m²) | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal range |
| 25.0 to 29.9 | Overweight (pre-obese) |
| 30.0 to 34.9 | Obesity class I |
| 35.0 to 39.9 | Obesity class II |
| 40.0 and above | Obesity class III |
Sources and disclaimer
Categories: World Health Organization, "A healthy lifestyle: WHO recommendations" and the WHO Global Database on BMI. Children: CDC, "About Child and Teen BMI". The 703 factor for pounds and inches is the CDC adult BMI formula.
This tool is not medical advice. Ask a doctor about your own health.
Sources: WHO · WHO (healthy lifestyle) · CDCLast reviewed 2026-10-13
FAQ
Is BMI accurate for athletes?
Not always. Muscle weighs more than fat, so a muscular person can land in the overweight range with little body fat. Waist size and body fat percentage give extra context.
Can I use it for my child?
No. For ages 2 to 19 BMI is compared with percentiles for the child's age and sex (CDC or WHO growth charts), not with the adult cut-offs. This tool shows the number for under-18s but gives no category. Ask a pediatrician.
What BMI is considered healthy?
The WHO normal range for adults is 18.5 to 24.9. Some groups, including many people of Asian descent, may face higher health risk at lower BMI values, so local guidance can differ.
Is my data sent anywhere?
No. The calculation runs in your browser and nothing you enter is sent to a server.