BMI Calculator
Calculate body mass index from height and weight.
<18.5Normal
18.5–24.9Overweight
25–29.9Obese
30+
BMI is a general screening estimate, not a diagnosis — it doesn't account for muscle mass, age, or body composition. For anything health-related, talk to a doctor.
Check your body mass index from height and weight
BMI Calculator divides your weight by the square of your height to give a body mass index, then shows which of the standard adult categories that number falls into. You can enter metric or imperial measurements.
BMI is a rough screening figure, not a health assessment, and nothing on this page is medical advice. The tool shows only the number and its category label, and your height and weight stay in your browser.
How to calculate BMI
- Choose Metric (cm / kg) or Imperial (ft-in / lb).
- For metric, enter height in centimetres and weight in kilograms. For imperial, enter height in feet and inches and weight in pounds.
- Click Calculate BMI to see the result and the category scale.
- Switching units clears the result, and numbers typed in one system aren’t carried over to the other, so enter them again.
Reading your BMI result
The BMI is shown to one decimal place with its category underneath, followed by a scale of the four adult bands used by the World Health Organization:
- Underweight: below 18.5
- Normal weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obese: 30 and above
When a BMI figure is useful
- Before an appointment: know the number a doctor or nurse may mention, and ask them what it means for you specifically.
- Watching a trend: compare your own BMI over months as a broad indicator, rather than reading much into a single result.
- Questionnaires: some insurance, fitness or health forms ask for BMI directly.
What BMI can and can’t tell you
How BMI is calculated
BMI is weight in kilograms divided by height in metres squared. Someone 170 cm tall who weighs 65 kg has a BMI of 65 ÷ 1.7², about 22.5. With pounds and inches, the same idea is multiplied by 703 to make the units work out.
The limits of a height-and-weight measure
BMI can’t tell muscle from fat or show where fat is carried, so muscular people can read as overweight and people with little muscle can read as normal. The standard bands are meant for adults; children and teenagers are assessed with growth charts that account for age and sex, and some health bodies use different cut-offs for certain populations.
This calculator has no age or sex input and applies the adult bands to everyone. Use the result as a starting point for a conversation with a health professional, not as a diagnosis.
BMI Calculator: common questions
Is a BMI of 25 overweight?
On the standard adult scale, 25 is where the Overweight band begins and 30 is where Obese begins. A result near a boundary means little on its own — a health professional can put it in context.
Can I use it for a child or teenager?
Not reliably. It uses the adult bands and doesn’t ask for age or sex, which children’s BMI depends on. A doctor or school nurse can check a child’s measurements against a growth chart.
Why does my BMI say overweight when I’m fit?
BMI uses only height and weight. Muscle is dense, so athletic people often have a higher BMI without carrying extra body fat.
Why isn’t a result appearing?
A result only shows when both height and weight are above zero. Check that both boxes are filled in for the unit system currently selected.
Do I need to convert my measurements first?
No. Choose Imperial to enter feet, inches and pounds directly. If a form wants metric figures, the Unit Converter can turn inches or pounds into centimetres or kilograms.
Are my height and weight saved anywhere?
No. The BMI is calculated in your browser and the numbers aren’t stored or sent. The Calculators category has the site’s other number tools.