How this calculation works
BMI compares weight with height using standardized adult screening categories. The categories shown follow CDC adult categories: below 18.5, 18.5 to under 25, 25 to under 30, and 30 or more.
BMI = weight in kilograms ÷ (height in metres)²A worked example
An adult weighing 70 kg at 175 cm has a BMI of approximately 22.86 kg/m².
Good to know
For adults aged 20 and older. Not for child growth assessment, pregnancy assessment or diagnosis. BMI does not directly measure body fat; interpretation can differ by individual and population.
A centimetre-to-metre conversion gets squared
Height appears squared in the denominator. Entering 175 cm corresponds to 1.75 m, whose square is 3.0625 m². A weight of 70 kg divided by that value gives approximately 22.86 kg/m². Using 175 directly as metres would introduce a factor-of-10,000 error.
The input labels handle the conversion for you: supply centimetres and kilograms. The result is a numerical screening measure, not a direct measurement of fat, muscle, fitness or an individual’s overall health.
A category boundary is not a sudden biological change
Two numerical BMI values can sit very close together while falling on opposite sides of a category boundary. A person’s situation does not abruptly change because a rounded display crosses a threshold. Use the result as one piece of context rather than a verdict.
The categories shown are the stated adult screening categories. They are not a child-growth assessment and do not replace an individual clinical interpretation. The method and reference link above make the scope visible rather than treating one number as a complete personal assessment.
A few questions, answered
Does this tell me my body-fat percentage?
No. BMI is calculated from weight and height and does not directly measure body composition.
Can I use the adult categories for a child?
No. Child and teen assessment uses age- and sex-specific methods; this tool is for adults aged 20 and older.