Free health tool
BMI Calculator
Enter your height and weight to get your Body Mass Index, your weight category, and the healthy weight range for your height. Everything runs in your browser — nothing is sent anywhere.
Key facts about BMI
BMI is weight in kilograms divided by height in metres squared. The World Health Organization's adult classification — also used by the CDC for adults 20 and older — applies to both men and women.
Adult BMI categories
How BMI is read by age group
| Group | How it's assessed | Healthy / lowest-risk |
|---|---|---|
| Children & teens (2–19) | BMI-for-age percentile, by sex | 5th to under 85th percentile |
| Adults (20–64) | Fixed adult bands | 18.5 – 24.9 |
| Older adults (65+) | Adult bands, interpreted with care | Lowest risk seen around 23 – 29.9 |
| Asian adults | Lower action points suggested | 18.5 – 22.9 (risk rises from 23) |
Children's results use CDC BMI-for-age growth charts. A meta-analysis of 32 studies in adults over 65 found the lowest mortality at BMI 23–29.9, and a WHO expert consultation published in The Lancet recommended lower action points for Asian populations.
Limitations of BMI
- It doesn't measure body fat. In a study of over 13,000 adults, BMI ≥30 missed about half of people with excess body fat.
- Muscle counts as weight. Athletes can score "overweight" while lean.
- Fat location matters. Belly fat carries more risk; waist-to-height ratio predicts heart and metabolic risk better than BMI. Aim for a waist under half your height.
- Age, sex and ethnicity change the picture, as the table above shows.
- Not for pregnancy or people with major fluid shifts or amputations.
Even so, large studies such as the Global BMI Mortality Collaboration (10.6 million adults) confirm BMI is a useful population-level screening tool. Use it as a starting point and discuss results with a health professional.
What your BMI means
Body Mass Index (BMI) is a simple measure that compares your weight to your height. The World Health Organization uses it worldwide to group adults into weight categories. It is a quick screening signal, not a diagnosis of body fatness or health.
| Category | BMI range |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity | 30.0 and above |
How BMI is calculated
BMI is your weight in kilograms divided by the square of your height in meters: BMI = kg / m². If you use pounds and inches, the formula is BMI = 703 × lb / in². This calculator does the conversion for you — just switch between metric and imperial units above.
What BMI doesn't tell you
BMI can't tell the difference between muscle and fat, so athletes and very muscular people often score "overweight" despite low body fat. It also applies the same ranges to all adults regardless of sex, and it isn't meant for children, pregnant women, or adults over 65 without clinical interpretation. Where your body stores fat matters too — fat around the waist carries more health risk than fat elsewhere.
What to do with your result
A BMI outside the healthy range is a good reason to talk to your doctor or a registered dietitian — especially alongside factors like blood pressure, blood sugar, and activity level. If your BMI is in the healthy range, keep doing what works: regular movement, decent sleep, and a balanced diet.
Frequently asked questions
Is this BMI calculator free?
Yes. Calculating your BMI, weight category, and healthy weight range costs nothing, and there's no sign-up.
Which units can I use?
Both. Switch between metric (cm and kg) and imperial (ft, in and lb) at the top of the calculator — the result updates instantly either way.
What is a healthy BMI?
For most adults, the WHO considers a BMI between 18.5 and 24.9 healthy. Below that is underweight, 25–29.9 is overweight, and 30 or above is obesity.
Is BMI accurate for everyone?
No. BMI is a population-level screening tool. It overestimates body fat in muscular people and can underestimate it in older adults who have lost muscle. Use it as a starting point, not a verdict.
Is my data stored?
No. The calculation happens entirely in your browser — your height and weight never leave your device.