Enter your height and weight to see your Body Mass Index, your BMI category, and the healthy weight range for your height.
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What Is BMI?
Body Mass Index (BMI) is a simple measure that compares your weight with your height. It's one of the most widely used screening tools for checking whether your weight falls within a healthy range. The calculator above gives you your BMI, your category and the healthy weight range for your height in seconds.
How Is BMI Calculated?
BMI is your weight in kilograms divided by your height in metres, squared. In imperial units, it's your weight in pounds divided by your height in inches squared, multiplied by 703. For example, someone who is 170 cm tall and weighs 68 kg has a BMI of about 23.5.
Understanding Your BMI Result
For adults aged 20 and over, the World Health Organization uses these categories:
| 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 |
Some health bodies, including NICE in the UK, recommend lower thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, with 23 marking overweight and 27.5 marking obesity. This is because health risks can rise at a lower BMI in these groups.
If your BMI falls outside the healthy range, it's worth discussing with a healthcare provider rather than making changes based on this number alone.
Why BMI Isn't the Whole Picture
BMI is a useful starting point, but it has real limits. It can't tell muscle from fat, so athletes and very muscular people can have a high BMI without carrying excess fat. It also doesn't show where fat is stored, and fat around the waist is more closely linked to health risks than fat elsewhere.
For a fuller picture, pair your BMI with other measures:
- Waist-to-height ratio: a simple guideline is to keep your waist measurement to less than half your height.
- Waist circumference: measured around your middle, just above the hip bones.
- A conversation with your doctor, who can consider your health history, blood pressure and other factors.
BMI for Children and Teens
Adult BMI categories don't apply to anyone under 20. Children's body fat changes as they grow and differs between boys and girls, so their BMI is compared with others of the same age and sex using growth charts. If you enter an age under 20, this calculator shows the BMI number only. For a proper assessment, use the CDC Child and Teen BMI Calculator or speak to your child's doctor.
Frequently Asked Questions
Is BMI accurate for everyone?
No. BMI works reasonably well as a general screening tool for most adults, but it's less reliable for athletes, older adults, pregnant women and children, because it can't tell the difference between muscle, fat and bone.
What's a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. The calculator shows the matching healthy weight range in kilograms or pounds for your height.
I'm muscular. Why does my BMI say I'm overweight?
Muscle is denser than fat, so people with a lot of muscle can have a high BMI even with low body fat. In this case, waist measurement or a body fat assessment gives a more accurate picture.
Does ethnicity affect healthy BMI?
It can. Health risks may start at a lower BMI for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, so some guidelines use 23 and 27.5 as the thresholds for overweight and obesity.
Can I use this BMI calculator for my child?
This calculator is designed for adults. Children and teens under 20 are assessed using age- and sex-specific BMI percentiles, so a child and teen BMI calculator or your child's doctor will give a more accurate result.
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This calculator gives general estimates for information only and is not medical advice. Talk to a doctor or qualified health professional about your weight and health.