BMI Calculator US
Calculate your Body Mass Index from height and weight, with your local units.
How it works
BMI compares your weight to your height as a general screening number. It is the same formula worldwide; only the units differ.
BMI = weight (kg) ÷ height (m)²- Under 18.5 = underweight
- 18.5–24.9 = healthy
- 25–29.9 = overweight
- 30+ = obese
BMI guides & tutorials
Frequently asked questions
How is BMI calculated?
In US units, multiply your weight in pounds by 703, then divide by your height in inches squared. In metric units, divide weight in kilograms by height in metres squared.
What are the BMI categories?
For adults: under 18.5 is underweight, 18.5–24.9 is healthy, 25–29.9 is overweight, and 30 or above is obese, according to the CDC and WHO.
Is BMI an accurate measure of health?
It is a screening tool, not a diagnosis. It does not distinguish muscle from fat or account for age, sex and ethnicity, so it should be interpreted alongside other measures.
Why might an athlete have a high BMI?
Muscle is denser than fat, so very muscular people can have a high BMI while carrying little body fat. BMI cannot tell the two apart.
Does BMI work the same for children?
No. For children and teens, BMI is interpreted using age- and sex-specific percentile charts rather than the fixed adult categories.
What should I do if my BMI is outside the healthy range?
Use it as a prompt to look at the bigger picture and, if you have concerns, speak with a doctor or qualified healthcare professional who can advise based on your individual circumstances.
How BMI is calculated
Body Mass Index is a simple screening number that relates your weight to your height. With US units the formula is BMI = 703 × weight (lb) ÷ height (in)2; in metric units it is weight in kilograms divided by height in metres squared. It gives a single figure that places you into a broad weight category.
Standard categories
The CDC and WHO use the same adult ranges: below 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25.0 to 29.9 is overweight, and 30.0 and above is classified as obese. For example, a person who is 5’9” (69 in) and weighs 160 lb has a BMI of about 23.6, which sits in the healthy range.
What BMI does not capture
BMI is a useful population-level screening tool, but it does not measure body fat directly and cannot tell muscle from fat. Very muscular people (athletes, for instance) can read as "overweight" despite low body fat, while the figure may understate fat in older adults who have lost muscle. It also does not account for differences across age, sex, or ethnic background.
Using it sensibly
Treat BMI as one starting indicator, not a diagnosis. Measures such as waist circumference, body-fat percentage, and overall health markers give a fuller picture. If you have any concerns about your weight or health, a doctor or qualified healthcare professional can interpret these numbers in the context of your individual situation.
Results are estimates for general guidance in United States and may not reflect the latest local rates, fees or rules. Check official sources before making decisions.