What is BMI?
Body mass index (BMI) compares your weight with your height. It's used worldwide as a quick way to check whether a person's weight is in a healthy range for adults. It's simple to calculate and doesn't need any special equipment.
The BMI formula
BMI = weight (kg) ÷ height (m)²
BMI = 703 × weight (lb) ÷ height (in)²
Example
Someone who is 175 cm tall and weighs 70 kg has a BMI of 70 ÷ 1.75² = 22.9, which is in the healthy range.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obesity class I |
| 35 – 39.9 | Obesity class II |
| 40 and above | Obesity class III |
Limitations of BMI
BMI doesn't measure body fat directly. Athletes with a lot of muscle may be classed as overweight, and people who have lost muscle may look healthy by BMI while carrying too much fat. Use it alongside other measures such as waist circumference or our body fat calculator, and talk to a doctor about your health.
