How we calculate

The calculators share one engine with unit tests. Reference data and official rules are kept in files with their source, the date they were fetched or checked, and a list of open points; the pages are generated from those files.

Adult BMI

BMI is weight in kilograms divided by the square of height in metres, or 703 × pounds ÷ inches². The result is rounded to one decimal and the category is read from that rounded number, so the figure and its label always agree. The cut-offs (18.5, 25, 30) are the ones WHO, CDC and NHLBI publish for adults aged 20 and over.

Children and teens

For ages 2 to 20 the BMI is compared with the CDC growth charts. Up to the 95th percentile the percentile comes from CDC's L, M and S values for the child's sex and age; above it we use CDC's extended method from 2022. The values are read from CDC's two published data files, stored unchanged with a checksum, and interpolated by age between two rows of the table.

Army standard

The rule, its rounding steps and the table of limits are stored in one versioned file with links to the directive and the measurement guidance. The build stops if that file has not been re-checked for 120 days. See the Army calculator for the current status.

Rounding

BMI is shown to one decimal, child percentiles as whole numbers rounded down, weights to the pound or a tenth of a kilogram. A healthy weight range lists only weights whose rounded BMI falls inside 18.5 to 24.9.

What the results are not

A BMI or a waist ratio is a screening measure. It does not measure body fat, and it does not replace an assessment by a health professional or an official Army measurement.

Where the calculation happens

In your browser. The page downloads the tool once and does the work on your device, so results appear as you type and your inputs are not sent to us.

What a tool page shows

The date the page was last updated.
How the result is produced.
On the tools rebuilt on our current template: the formula or rule, a worked example you can check by hand, and the sources the numbers come from, linked. Older tools are being brought up to that standard.

Sources we rely on

Limits

BMI360 gives general information, not medical advice, a diagnosis or an official Army record. If a result worries you, or you are thinking about changing your weight, talk to a doctor, a pediatrician or a registered dietitian. If thoughts about weight or eating are taking over your day, a health professional can help with that too.