BMI Calculator: How to Calculate and Understand Your BMI
Body mass index, or BMI, is a quick screening number that compares your weight with your height. A BMI Calculator works it out in seconds from your height in centimeters and weight in kilograms.
How is BMI calculated?
BMI equals your weight in kilograms divided by your height in meters, squared. For example, someone who is 170 cm tall and weighs 65 kg has a BMI of about 22.5.
What do the categories mean?
- Under 18.5: underweight.
- 18.5 to 24.9: healthy weight.
- 25 to 29.9: overweight.
- 30 or more: obesity.
The calculator shows your number, your category and a marker on a color bar.
How to use the calculator
- Enter your height in centimeters.
- Enter your weight in kilograms.
- Press Calculate BMI and read your result.
What BMI cannot tell you
BMI is only a screening tool, not a diagnosis. It does not measure body fat, and it ignores several things.
- Muscle: athletes can have a high BMI with little body fat.
- Age and sex: healthy ranges can differ between people.
- Where fat is carried: waist size can matter more than the total number.
- Health conditions and ethnicity: risk levels can vary for different groups.
Using your result sensibly
- Treat BMI as one clue, alongside waist size, activity, diet and family history.
- Do not make big changes to your diet or exercise based only on a number.
- Talk to a doctor or dietitian if your result concerns you, or if you want a plan that suits you.
Children and teenagers
This calculator uses adult categories. For anyone under 18, growth charts and a health professional give a more accurate picture.
A quick example
Enter 170 for height and 65 for weight. The calculator shows 22.5, places the marker in the healthy range, and labels it Healthy weight. Try changing the weight to see how the number and category move, which helps you understand how BMI responds to small changes.
Free and private
The calculator runs in your browser. Your height and weight are never stored or sent anywhere, and there is no sign up or login.
Frequently asked questions
Can I enter feet and pounds? The tool uses centimeters and kilograms. Convert your values first with the Unit Converter.
Is a healthy BMI the same as being healthy? No. Many things affect health, and BMI shows only part of the picture. This page is general information, not medical advice.