Purpose and context
What does the BMI Calculator do?
BMI relates body weight to height. It is widely used as an adult screening measure because it is simple and reproducible, but it does not directly measure body fat or diagnose health.
Who it supports: Adults age 20 and older. Youth interpretation requires age- and sex-specific growth-chart percentiles that this tool does not implement.
Transparent calculation
Formula and calculation method
The calculator converts weight to kilograms and height to metres, divides weight by squared height, retains full internal precision, and displays one decimal place.
Worked calculation example
At 70 kg and 1.75 m, BMI = 70 ÷ (1.75 × 1.75) = 22.86, displayed as 22.9 kg/m².
The live calculator retains greater internal precision and rounds only when presenting the result.
How to use the BMI Calculator
- Choose metric or imperial units.
- Enter age, measured height and current weight.
- Calculate BMI and read both the value and screening category.
- Use the limitations and related tools for context.
Understanding your result
The result card identifies the value, unit, method, supporting values and an accuracy notice. Estimated and predicted outputs are labelled so that apparent precision is not mistaken for certainty.
Continue with the BMI Prime Calculator for a related measurement using its own documented method.
Accuracy, assumptions and limitations
Muscularity, pregnancy, fat distribution, age-related body-composition changes and individual clinical context can make BMI less informative.
Common input and interpretation mistakes
- Applying adult categories to people under 20.
- Entering centimetres as metres or pounds as kilograms.
- Treating BMI as a direct body-fat measurement.
Primary method source: https://www.cdc.gov/bmi/adult-calculator/bmi-categories.php.
Frequently asked questions about BMI Calculator
Body Mass Index is weight in kilograms divided by height in metres squared. It is an adult screening measure, not a diagnosis.
CDC adult categories describe 18.5 to less than 25 kg/m² as the healthy-weight screening range.
No. BMI uses only height and weight, so it cannot directly measure fat mass, muscle mass or fat distribution.
High muscle mass can raise body weight and BMI without representing the same body-fat level seen in a less muscular person.
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