Body mass index (BMI) is a quick screening number that compares your weight to your height. Enter your height and weight in US or metric units to see your BMI, the adult category it falls in, and a plain-language explanation of what that does and does not mean. This tool is for adults 20 and older who are not pregnant.
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Estimates are educational. They do not diagnose any condition and do not establish eligibility for any medication. A licensed provider decides what is appropriate for you. Explore treatments if you want to learn about provider-guided programs.
BMI estimates whether your weight is in proportion to your height. It is used by public health agencies because it is cheap, fast and correlates with body fat across large populations. It is a screening tool, not a diagnosis, and it does not measure body fat directly.
The formula is weight in kilograms divided by height in meters squared:
BMI = weight (kg) ÷ height (m)²
If you enter pounds and inches, the calculator converts them first (1 lb = 0.4536 kg, 1 in = 2.54 cm), so the result is the same in either unit system. Adult categories follow the CDC and WHO cutoffs: underweight below 18.5, healthy weight 18.5 to 24.9, overweight 25.0 to 29.9, and obesity 30.0 or higher, divided into class 1 (30.0 to 34.9), class 2 (35.0 to 39.9) and class 3 (40.0 or higher).
Not very. Muscle is denser than fat, so a person with a lot of muscle can have a BMI in the overweight or obesity range while having low body fat. BMI is most useful as a population screening tool, not an individual body fat measurement.
The CDC and WHO define a healthy weight range as a BMI of 18.5 to 24.9. Values below 18.5 are classified as underweight, 25.0 to 29.9 as overweight, and 30.0 or above as obesity.
No single number decides that. Prescribing information for weight management medications references BMI alongside other factors, and a licensed provider reviews your health history, other conditions and goals before deciding whether any treatment is appropriate. This calculator is educational only.
No. Children and teens aged 2 to 19 are assessed with age- and sex-specific BMI percentiles. The CDC offers a separate calculator for that age group.
Because the calculator converts your entries to kilograms and meters before applying the formula. Switching the unit toggle converts the numbers you already typed, so the result stays the same.
A change of a few tenths of a point usually reflects normal fluctuation in weight. Trends over months matter more than any single reading, and how you feel, your strength and your lab results all matter alongside the number.
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