BMI Calculator

What is bmi calculator?

Body mass index is a quick screening number that compares weight with height. Doctors and health surveys use it because it is simple, not because it is perfect.

BMI does not measure body fat, muscle, bone density or where fat is stored. An athlete with a lot of muscle can have a high BMI and be healthy, while someone with a normal BMI can still have health risks.

How to use the bmi calculator

1. Choose metric or imperial.
2. Enter your height (centimeters or inches) and weight (kilograms or pounds).
3. Press Calculate to see your BMI and the matching category.

How the bmi calculator works

In metric, BMI is weight in kilograms divided by height in meters squared. In imperial, it is 703 times weight in pounds, divided by height in inches squared. The categories follow the World Health Organization adult ranges.

Worked example

Common uses of the bmi calculator

• Getting a quick screening number before a health check.
• Tracking weight changes over time alongside waist size and fitness.
• Setting a realistic weight range for your height as a starting point.
• Completing forms for fitness programs or insurance that ask for BMI.
• Learning what the WHO categories mean.

Tips and common mistakes

Use BMI as one data point and speak with a doctor about waist size, diet, activity and family history.

This calculator is for adults. Children and teenagers need age and sex specific growth charts.

Background: what to know before you rely on it

Body mass index was created in the 1830s by the Belgian mathematician Adolphe Quetelet to describe populations, not individuals. It became a common screening tool in the twentieth century because it needs only height and weight. Its limits are well known. It cannot tell muscle from fat, it ignores where fat is stored and ranges can differ by age, sex and ethnic group. A very muscular person can have a high BMI and low health risk. Doctors therefore use BMI together with waist size, blood tests, activity and family history. If your result worries you, speak with a health professional rather than relying on a single number.

Private, free and fast

This tool runs entirely in your browser. What you type or choose is not uploaded to a server and is not saved after you close the page, which keeps it fast and private. It is free to use as often as you like. See more in all calculators, or browse the full list of tools.

Related tools

Results are for information and education. For legal, financial, medical or security decisions, check with a qualified professional. Financial results are estimates and exclude fees and taxes unless the tool says otherwise.