Free tool
BMI calculator
Enter your height and weight to see your body mass index (BMI) and what it means. For adults 20 and older.
What is BMI?
Body mass index, or BMI, compares your weight to your height. Doctors use it as a quick first check to see if weight might affect your health. It's a screening tool, not a diagnosis.
The math is simple: your weight in kilograms divided by your height in meters, squared. In US units, it's weight in pounds times 703, divided by height in inches squared.
What the numbers mean
These are the adult categories used by the CDC:
| BMI | Category |
|---|---|
| Under 18.5 | Underweight |
| 18.5 to under 25 | Healthy weight |
| 25 to under 30 | Overweight |
| 30 to under 35 | Obesity, class 1 |
| 35 to under 40 | Obesity, class 2 |
| 40 or higher | Obesity, class 3 (severe) |
What BMI can't tell you
BMI doesn't know how much of your weight is muscle or where you carry fat. A very muscular person can have a high BMI and be healthy. An older adult can have a "normal" BMI and still have too little muscle. That's why your doctor may also check your waist size, blood pressure, blood sugar, and cholesterol.
Common questions
Is BMI accurate?
It's a good quick check for most adults, but it doesn't measure body fat directly. Use it as a starting point for a talk with your doctor, not a final answer.
Does this work for kids and teens?
No. Children and teens 2 to 19 use BMI percentiles based on age and sex. Use the CDC's child and teen calculator or ask your child's doctor.
Should I worry if my BMI is over 25?
Not on its own. It's a sign to look at other health numbers too. Even losing 5% of your weight can improve blood pressure and blood sugar for many people.
Does BMI differ by race or ethnicity?
Some groups, including many people of Asian descent, can face higher health risks at lower BMIs. Your doctor can help you understand what your number means for you.
A note on safetyThis tool gives general estimates for healthy adults. It isn't medical advice. If you're pregnant, under 18, have a health condition, or take medicine that affects your weight or fluids, ask your doctor what's right for you.