What is BMI?
Body mass index is a number that compares your weight with your height. It is a quick screening tool that groups adults into categories linked to health risks. It is not a diagnosis and it does not measure body fat directly.
The formula is weight in kilograms divided by height in metres squared. In pounds and inches it is 703 x weight / height squared. Example: 70 kg at 175 cm gives 70 / 3.0625, which is a BMI of about 22.9.
How to use this BMI calculator
- Choose metric or imperial units.
- Enter your height and weight. Age is optional.
- Press Calculate to see your BMI, your category and the healthy weight range for your height.
Healthy weight range
A BMI between 18.5 and 24.9 is classed as normal weight for adults. Multiplying those values by your height squared gives the weight range for your height. At 175 cm, that is about 56.7 kg to 76.3 kg. The calculator works this out for you and shows how far you are from the range.
Limits of BMI
- BMI does not separate muscle from fat, so very muscular people can score as overweight.
- It does not show where fat is stored. Waist size is another useful measure.
- Age, sex and ethnicity change what a healthy BMI looks like. Some health bodies suggest lower action points for South Asian adults, because health risk can rise at a lower BMI.
- For children and teenagers, BMI must be compared with age and sex growth charts, so ask a doctor.
What to do with your result
Use the number as a starting point for a conversation with a doctor or dietitian, not as a verdict. If your BMI is outside the normal range, look at the full picture, including diet, activity, waist size, family history and blood tests. This page is for information and is not medical advice.
Adult BMI categories (WHO)
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25.0 to 29.9 | Overweight |
| 30.0 to 34.9 | Obesity, class I |
| 35.0 to 39.9 | Obesity, class II |
| 40.0 and above | Obesity, class III |
Frequently Asked Questions
How is BMI calculated?
Divide your weight in kilograms by your height in metres squared.
What is a healthy BMI?
For adults, 18.5 to 24.9 is considered the normal range.
Is BMI accurate for athletes?
Not always. Muscle weighs more than fat, so athletes can have a high BMI with low body fat.
Can I use BMI for children?
No. Children and teens need age and sex specific growth charts.
Does BMI work the same for every ethnic group?
Not exactly. Health risks can differ between groups, and some health bodies suggest different cut-offs for South Asian adults. Ask a healthcare professional.
Is my data stored?
No. The calculation runs in your browser, so the numbers you enter are not sent to our server.