How to use the BMI calculator
- Choose metric (centimetres and kilograms) or imperial (feet, inches and pounds).
- Enter your height and weight. Your BMI and category appear instantly.
- Check the healthy weight range — the weights that would give a BMI of 18.5–24.9 at your height.
BMI categories for adults
| BMI | Category (WHO) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40 and above | Obesity class III |
How BMI is calculated
Body Mass Index divides your weight by the square of your height:
BMI = weight (kg) ÷ height (m)². In imperial units the formula is
BMI = 703 × weight (lb) ÷ height (in)². For example, a person 1.70 m tall weighing 68 kg
has a BMI of 68 ÷ (1.70 × 1.70) = 23.5, which falls in the healthy range.
What BMI does and does not tell you
BMI was designed in the 19th century as a simple way to compare populations, and it remains useful because it is quick, free and correlates reasonably well with body fat for most people. Doctors use it as a first screening step for weight-related health risks such as type 2 diabetes, high blood pressure and heart disease.
It has real limits, though. BMI cannot tell muscle from fat, so muscular people may be classed as overweight. It says nothing about where fat is stored — fat around the waist carries more health risk than fat elsewhere — and it does not account for age, sex or ethnicity. Waist circumference, waist-to-height ratio and body-fat measurements give a fuller picture. Treat your BMI as a starting point for a conversation with a health professional, not as a verdict.
This calculator is for general information only and is not medical advice.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight range by the World Health Organization.
Is BMI accurate for everyone?
BMI is a quick screening tool, not a diagnosis. It does not distinguish muscle from fat, so athletes may score as "overweight", and it can underestimate body fat in older adults. Ask a doctor for a full assessment.
Can children use this calculator?
No. Children and teenagers (under 20) need BMI-for-age percentiles, which compare them with others of the same age and sex. Ask a pediatrician.
Are the categories different for Asian populations?
Some health authorities use lower cut-offs for people of Asian descent, for example overweight from 23 and obesity from 27.5, because health risks appear at lower BMI values.
Is my data stored?
No. The calculation happens in your browser and nothing is saved or sent anywhere.