Use this free BMI calculator to work out your body mass index and see whether you’re in a healthy weight range for your height. It works in kilograms and centimetres or pounds and feet.
BMI Calculator
Work out your body mass index (BMI) and the healthy weight range for your height.
| Healthy weight range for your height | |
| Your height |
BMI is a quick screening tool, not a diagnosis. It doesn’t measure body fat directly, so very muscular people may get a higher BMI than their health suggests. Talk to your doctor if you have any concerns about your weight.
What Is BMI?
Body mass index (BMI) is a simple measure that compares your weight to your height. It’s calculated by dividing your weight in kilograms by your height in metres squared (kg/m²). Doctors use it as a quick way to check whether someone may be underweight, a healthy weight, overweight or obese.
Adult BMI Categories
These are the standard categories for adults, used by the CDC and the World Health Organization:
| 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 or above | Obesity (class 3) |
Lower Cut-Offs for Some Ethnic Backgrounds
People of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background have a higher risk of health problems like type 2 diabetes at a lower BMI. The NHS recommends lower cut-offs for these groups, so if this applies to you, use these values instead of the standard ones:
| BMI | Category |
|---|---|
| 23 to 27.4 | Overweight |
| 27.5 or above | Obese |
Limitations of BMI
- It doesn’t measure body fat. Muscular people can have a high BMI without having excess fat.
- It doesn’t show where fat is stored. Fat around your stomach carries more health risk.
- It isn’t for everyone. BMI isn’t suitable for children, pregnant women or some older adults in the same way.
- Check your waist too. A simple rule of thumb is to keep your waist measurement less than half your height.
What to Do With Your Result
If Your BMI Is Above the Healthy Range
Small changes add up. Losing even 5% of your body weight can improve your health. Use our calorie calculator to set a daily target, and read how much weight you can safely lose in a month and how to lose belly fat naturally.
If Your BMI Is Below 18.5
You may need to gain some weight. See our guides to healthy high-calorie foods for weight gain and gaining weight with a fast metabolism, and speak to a doctor if you’ve lost weight without trying.
If You Are in the Healthy Range
Keep active, eat a balanced diet and get enough protein to maintain your muscle. Our protein calculator shows how much you need.
Frequently Asked Questions
What is a healthy BMI?
For most adults, a BMI of 18.5 to 24.9 is considered healthy. For people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, the NHS suggests aiming for below 23.
Is BMI accurate?
BMI is a useful screening tool for most people, but it can overestimate body fat in muscular people and underestimate it in people who have lost muscle. Use it alongside your waist measurement and advice from your doctor.
How do I calculate BMI by hand?
Divide your weight in kilograms by your height in metres squared. For example, 70 kg ÷ (1.75 m × 1.75 m) = 22.9. In pounds and inches, multiply your weight in pounds by 703 and divide by your height in inches squared.
Can I use this BMI calculator for children?
No. Children and teenagers need age- and sex-specific growth charts. Please ask your doctor.
Related Tools and Articles
- Body Fat Calculator: Estimate Your Body Fat Percentage
- Calorie Calculator: How Many Calories Do You Need a Day?
- Protein Calculator: How Much Protein Do You Need a Day?
- How Much Weight Can You Lose in a Month?
- How to Lose Weight Fast in 2 Weeks (Safely)
Sources
This BMI calculator is for adults aged 18 and over and is for general information only. It isn’t a diagnosis. Please speak to your doctor for advice about your weight and health.