BMI Calculator
Get your body mass index from your weight and height in seconds.
Learn how it works: How Is BMI Calculated?Enter your weight and height to see your BMI.
How to use the BMI calculator
BMI takes two numbers: your weight and your height. Here is how to get your result in a few seconds.
- Pick your unit system. Metric uses kilograms and centimeters. Imperial uses pounds, feet, and inches.
- Enter your weight.
- Enter your height.
- Read your BMI and category on the right. The number updates as you type.
What is BMI?
BMI stands for body mass index. It compares your weight to your height and gives you one number. Doctors and researchers use it as a quick screening tool. It works well for large groups and population studies.
BMI has real limits. It does not measure body fat directly. It does not separate muscle from fat. A strong athlete and a person with little muscle can share the same BMI. Age, sex, and background also shift what counts as healthy. Read BMI as a starting point, not a diagnosis. For a full picture, talk to a doctor who can check other markers.
BMI categories explained
The World Health Organization splits adult BMI into four ranges:
| Category | BMI range |
|---|---|
| Underweight | Below 18.5 |
| Normal | 18.5 to 24.9 |
| Overweight | 25 to 29.9 |
| Obese | 30 and above |
These ranges apply to most adults aged 20 and over. They do not apply to children, who use age and sex charts instead.
BMI formula
The metric formula is simple:
BMI = weight (kg) / height (m)²
Say you weigh 70 kg and stand 1.75 m tall. Square the height: 1.75 × 1.75 = 3.06. Then divide: 70 / 3.06 = 22.9. That BMI falls in the normal range.
For imperial units, the calculator converts first. It turns pounds into kilograms and feet plus inches into meters, then runs the same formula. You get the same result either way.
Frequently asked questions
- Is BMI accurate?
- BMI is a useful screen, not a precise measure. It flags possible weight risk for most adults. It can miss the mark for athletes and older people. Use it with other health checks.
- What is a healthy BMI?
- For most adults, a BMI between 18.5 and 24.9 counts as normal. Your ideal number can vary with age, muscle, and body type. A doctor can tell you what fits you.
- Does BMI work for athletes?
- Often no. Muscle weighs more than fat. A fit athlete can land in the overweight range while carrying very little fat. Body fat tests give a better read for them.
- Does BMI differ by age or sex?
- The adult ranges stay the same for men and women. But the meaning shifts. Older adults and women tend to carry more fat at the same BMI. Children use separate growth charts.
- How do I lower my BMI?
- Lower your weight through steady habits. Move more, eat whole foods, and sleep well. Building muscle while losing fat also helps. Ask a doctor before any big change.
- Is BMI used for children?
- Not the adult ranges. Kids and teens use BMI-for-age percentiles that account for growth. A pediatrician reads those charts.