Free browser tool · part of GentleTools Fitness

Body Fat % & BMI Calculator

Calculate adult BMI, waist-to-height ratio and a legacy circumference body-fat estimate with the same shared calculation engine used by the GentleTools Fitness ecosystem.

Adult-oriented calculator.BMI uses CDC adult categories for ages 20+. The tape-measure body-fat value is a legacy circumference estimate and is not the current U.S. Navy BCA method. The form does not impose an arbitrary upper age ceiling.
Tape measurements

Use a flexible, non-stretch tape. Keep it level and snug without compressing the skin. Small placement changes can materially change a circumference estimate, so use a consistent technique.

No sample measurements are inserted. After a successful calculation, age, sex, height and weight are kept in your local GentleTools Fitness profile so other tools can reuse them. Tape measurements are not added to that profile; the full calculation is stored only when you choose Save result.

Method notes

BMI categories follow the CDC adult categories for ages 20+. The circumference estimate uses the older neck/waist/hip logarithmic tape equations commonly associated with the legacy Hodgdon–Beckett/Navy method. Current Navy BCA guidance uses a different process, so this tool does not report Navy pass/fail status.

CDC adult BMI categories ↗Current Navy Physical Readiness guidance ↗

One calculator, clearer method labels

The previous version described its neck/waist/hip equation simply as the “U.S. Navy method.” That is no longer precise enough: current Navy Body Composition Assessment guidance uses a different process. This page preserves the classic circumference estimate for continuity and trend tracking while labeling it as a legacy estimate.

How to interpret the numbers

BMI compares weight with height and is a screening measure rather than a diagnosis. Waist-to-height ratio is reported as a raw ratio and percentage of height without turning a threshold from one organization into a universal health rule. The body-fat value is an estimate that is sensitive to tape placement and the equation itself.

Frequently asked questions

Is this the current U.S. Navy body composition test?

No. The tape equation is a legacy circumference estimate commonly associated with older Navy-style calculators. Current Navy BCA guidance uses a different process, so this page does not report Navy pass/fail status.

What BMI categories does this use?

For adults age 20 and older, it uses CDC adult BMI categories. BMI is a screening measure and should not be treated as a diagnosis.

What happened to my old saved entries?

They are not deleted or overwritten. If this browser contains entries from the previous version, they appear below the calculator in a read-only legacy archive that can be exported as JSON.