What Is BMI?
Body Mass Index (BMI) is a quick screening number that compares your weight with your height. Doctors and health organizations use it as a simple first check of whether a person's weight falls in a healthy range. This BMI calculator works in metric (kilograms and centimeters) or imperial (pounds, feet and inches) units and shows your result with its World Health Organization (WHO) category.
How BMI Is Calculated
Metric: BMI = weight (kg) ÷ height (m)². Imperial: BMI = 703 × weight (lb) ÷ height (in)².
Example: a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the normal weight range.
BMI Categories for Adults
These ranges apply to adults 20 and older. Children and teens are assessed with age- and sex-specific BMI percentiles instead.
- Underweight: below 18.5
- Normal weight: 18.5 to 24.9
- Overweight: 25.0 to 29.9
- Obese: 30.0 and above
Frequently Asked Questions
Is BMI accurate for athletes and muscular people?
Not always. BMI cannot tell muscle from fat, so very muscular people can be classed as overweight even with low body fat. Our Body Fat Calculator gives a better picture of body composition.
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight range. Your doctor may recommend a different target based on your age, ethnicity, health history and body composition.
Can BMI diagnose health problems?
No. BMI is a screening tool, not a diagnosis. It does not measure body fat directly or account for where fat is stored. Talk to a healthcare provider for a full assessment.