BMI Calculator
Work out your body mass index in metric or imperial units and see your weight category.
Runs in your browser — nothing is sent or saved.
How to work out your BMI
- Choose metric or imperial units.
- Enter your weight and height.
- Your BMI and its category show right away.
- Change a number to see the effect.
What BMI means
BMI stands for body mass index. It is your weight divided by your height squared, which gives one number that sorts most adults into a band. Under 18.5 is underweight. From 18.5 to 24.9 is a healthy weight. From 25 to 29.9 is overweight. From 30 up is obese. The tool shows your number and its band.
Where BMI falls short
BMI does not know muscle from fat. A fit person with a lot of muscle can score in the overweight band while carrying little fat, and a person with low muscle can score healthy while carrying more fat than is ideal. It also was built around adults, so it is not the right measure for children, who use age-based charts. Treat BMI as a rough first check, not a diagnosis.
Metric and imperial
The metric side asks for kilograms and centimetres. The imperial side asks for pounds and your height in feet and inches. Both use the same math underneath; only the units differ. So you get the same BMI either way.
The BMI categories (WHO)
These are the adult bands set by the World Health Organization:
| Category | BMI (kg/m²) |
|---|---|
| Underweight | below 18.5 |
| Healthy weight | 18.5 to 24.9 |
| Overweight | 25 to 29.9 |
| Obesity class 1 | 30 to 34.9 |
| Obesity class 2 | 35 to 39.9 |
| Obesity class 3 | 40 and above |
Source: World Health Organization (WHO) BMI classification for adults.
Children and teens use a different chart
For ages 2 to 20, BMI is read against age and sex percentile charts, not these fixed bands. The US Centers for Disease Control and Prevention (CDC) groups children as underweight below the 5th percentile, healthy weight from the 5th to the 85th, overweight from the 85th to the 95th, and obese at or above the 95th. Use a CDC growth chart for a child, since this tool is built for adults.
Source: US Centers for Disease Control and Prevention (CDC).
FAQ
What is a healthy BMI?
For most adults, 18.5 to 24.9 is the healthy range. Below that is underweight and above is overweight.
Is BMI accurate for athletes?
Not really. Muscle weighs more than fat, so a muscular person can read as overweight even when they are lean. Use it as a rough guide.
Does BMI work for children?
No. Children use age and sex based charts. This tool is meant for adults.
Which is better, metric or imperial?
Neither. Both give the same BMI. Pick the units you know best.
Is my weight and height sent anywhere?
No. The numbers stay in your browser and nothing is saved.
Is BMI different for women and men?
The formula is the same. BMI for women and BMI for men both divide weight by height squared, and the healthy range of 18.5 to 24.9 applies to both. Muscle can push athletes above it without extra fat.
What is my BMI supposed to be?
For most adults, between 18.5 and 24.9. Below that counts as underweight and above it as overweight in the standard bands doctors use.