BMI Calculator
Quickly calculate your Body Mass Index (BMI) and see which weight range it falls into.
BMI is a general indicator and doesn't replace a medical evaluation. Factors like muscle mass, age and body composition also affect health.
Body Mass Index (BMI) relates weight and height and is used by the World Health Organization as an initial reference to indicate whether someone is underweight, at a normal weight, overweight, or in a class of obesity. It's calculated by dividing weight in kilograms by height in meters squared. Because it's a quick, simple calculation, BMI is widely used in population research and initial screenings, but it has important limitations worth knowing before drawing conclusions about any one person.
How to use
- Enter your weight in kilograms.
- Enter your height in centimeters.
- See your calculated BMI and the matching category.
Worked example
Someone weighing 78 kg at a height of 1.75 m has a BMI of 78 ÷ (1.75 × 1.75) = 78 ÷ 3.0625 = 25.47. Since that value falls between 25 and 29.9, it lands in the range the WHO calls "overweight." That doesn't automatically mean excess body fat — it also depends on factors like muscle mass and fat distribution, which BMI alone doesn't capture.
Frequently asked questions
How is BMI calculated?
BMI is calculated by dividing weight (in kg) by height (in meters) squared: BMI = weight ÷ height².
Is BMI an exact measure of health?
No. BMI is a general, population-level indicator. It doesn't distinguish muscle mass from body fat, so athletes or very muscular people can have a high BMI without excess fat.
What are the BMI category ranges?
Per the WHO: below 18.5 is underweight; 18.5 to 24.9 is normal weight; 25 to 29.9 is overweight; 30 to 34.9 is obesity class I; 35 to 39.9 is obesity class II; and 40 or above is obesity class III.
Is BMI suitable for children, pregnant people, or older adults?
Not in the same way as for adults generally. Children and teenagers use age- and sex-specific BMI growth curves, pregnant people have expected weight gain from the pregnancy itself, and older adults may have different body composition due to natural muscle loss. These groups need a specific evaluation, not the standard adult chart.
What should I do if my BMI falls outside the 'normal' range?
BMI is just a starting point, not a diagnosis. If the result concerns you, the safest path is talking with a doctor or dietitian, who can weigh other factors — like waist circumference, lab tests, and health history — before drawing any conclusion.
Why can two people with the same BMI have very different health?
Because BMI doesn't distinguish where the weight comes from. Someone with more muscle mass and someone with more body fat can have the same BMI but quite different health risks. How fat is distributed in the body (for example, concentrated around the abdomen) also affects risk in ways BMI alone doesn't show.