How to use the BMI calculator
Choose metric or imperial units, then enter your height and weight. Your BMI, weight category and the healthy weight range for your height appear instantly.
The BMI formula
BMI = weight (kg) ÷ height (m)²
In imperial units: BMI = 703 × weight (lb) ÷ height (in)².
Example: someone who is 1.70 m tall and weighs 68 kg has a BMI of 68 ÷ (1.70 × 1.70) = 23.5, which is in the healthy range.
BMI categories for adults (WHO)
| BMI | Category |
|---|---|
| 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 |
Limitations of BMI
BMI is simple and useful for spotting trends, but it can't tell muscle from fat. Very muscular people, older adults and pregnant women may get misleading results. Use it as a starting point, and speak to a doctor or dietitian for personal advice.
This tool provides general information only and is not medical advice.
Frequently asked questions
What is a healthy BMI?
For most adults, the World Health Organization classes a BMI of 18.5 to 24.9 as a healthy weight. Under 18.5 is underweight, 25 to 29.9 is overweight and 30 or more is obese.
Is BMI accurate?
BMI is a quick screening tool, not a diagnosis. It doesn't distinguish muscle from fat, so athletes may score as overweight, and it doesn't show where fat is stored. Waist size and a doctor's check give a fuller picture.
Can children use this BMI calculator?
No. Children and teenagers need age- and sex-specific BMI percentile charts. This calculator is for adults aged 18 and over.
Are the cut-offs the same for everyone?
Some health bodies recommend lower cut-offs for people of Asian descent (for example, overweight from 23). Talk to a health professional about what's right for you.