How to use the BMI calculator
- Pick the unit you know for each one. Height can be in cm or feet and inches, and weight in kg, pounds or stones and pounds. You can mix them, for example height in feet and inches with weight in kg.
- Enter your height and weight. If you switch a unit after typing, the number is converted for you. For the most accurate result, weigh yourself in the morning without shoes.
- Your BMI, its category and the healthy weight range for your height appear straight away.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 to 34.9 | Obesity class 1 |
| 35 to 39.9 | Obesity class 2 |
| 40 and above | Obesity class 3 |
What BMI can and cannot tell you
BMI is popular because it is quick and needs only two numbers. Doctors use it as a first screening step, not a diagnosis. It does not measure body fat directly, and it says nothing about where fat is stored. Fat around the waist is linked to more health risks than fat elsewhere, so many doctors also check waist size. A simple guide: a waist measurement less than half your height is generally a good sign.
If you build muscle through sport or heavy work, your BMI may look high even though your body fat is low. On the other hand, someone with a normal BMI can still carry more body fat than is healthy. Use the number as one clue among several, alongside how you feel, how active you are and advice from your doctor.
This calculator gives general information and is not medical advice. If you are worried about your weight, please speak to a doctor or registered dietitian.