How to use this bmi calculator
Choose metric or US units, then enter an adult's current height and weight. Metric mode accepts kilograms and centimeters; US mode accepts pounds plus feet and inches. Check that the measurements were taken consistently, because clothing, shoes, rounding, and unit mistakes can change the result. The calculator converts US units internally before applying the same formula.
How the calculation works
Body mass index divides weight in kilograms by squared height in meters. Because height is squared, even a small height entry error can noticeably change the result. US measurements are converted using the exact international pound and inch definitions before the metric equation is evaluated.
For adults age 20 and older, CDC categories are underweight below 18.5, healthy weight from 18.5 to less than 25, overweight from 25 to less than 30, and obesity at 30 or above. A category is a screening label. BMI cannot distinguish fat from muscle, describe fat distribution, or account fully for age, disability, ethnicity, pregnancy, or athletic build.
Formulas
Metric BMI
US measurement form
Worked examples
Metric example
An adult who weighs 70 kg and is 175 cm tall has BMI = 70 ÷ 1.75² = 22.86. That falls in the CDC healthy-weight screening category.
US example
For 165 lb at 5 ft 10 in, BMI = 703 × 165 ÷ 70², approximately 23.67. Converting to kilograms and meters produces nearly the same result; tiny differences come from the rounded constant 703.
Common uses
Adult screening conversations
Calculate the standard height-to-weight index before a routine conversation with a qualified health professional. Bring the underlying measurements and avoid treating the category as a diagnosis.
Population and research context
Understand how reports group adult height and weight at a population level. BMI may be useful for broad comparisons even though it cannot describe an individual's body composition.
Measurement checks
Compare a manually calculated result with a form, record, or published example. Recheck height units and remove shoes before assuming a surprising value reflects a real change.
Accuracy and limitations
The calculator converts pounds with the exact international factor 0.45359237 and inches with the exact factor 2.54 centimeters, then applies the metric BMI equation. The displayed BMI is rounded to two decimal places.
BMI inherits limitations that arithmetic cannot fix. It is an adult screening index, not a direct assessment of fat, fitness, nutrition, disease, or an individually appropriate weight.
Sources and methodology
NumUtility uses the following primary or authoritative references for this calculator. Sources explain the method; they do not turn the result into personal medical advice.
Frequently asked questions
Is BMI a body-fat percentage?
No. BMI compares weight with squared height. It does not measure fat mass, muscle mass, bone density, or where body fat is carried.
Does this calculator work for children?
No. CDC evaluates BMI for children and teens with age- and sex-specific percentiles. This page uses adult categories and is intended for adults.
Can a muscular person have a high BMI?
Yes. BMI cannot separate muscle from fat, so some muscular adults may fall in a higher category despite having different body composition from another person with the same BMI.
Should I make a health decision from BMI alone?
No. Treat BMI as one screening measure and discuss concerns with a qualified health professional who can consider history, measurements, symptoms, and other relevant factors.
Are my health measurements stored?
No. Calculations run in your browser. NumUtility does not receive or save the values you enter in these tools.