Body Fat Calculator (US Navy Method)
Estimate body fat percentage from circumference measurements — no scale needed
Frequently Asked Questions
The US Navy method estimates body fat percentage from a handful of circumference measurements (waist, neck, and for women, hips) rather than requiring specialized equipment like calipers or a DEXA scan — a reasonably accurate, accessible estimation method, though one with real, documented limits on its precision.
Why circumference-based estimation works, with caveats
The US Navy method's formula was developed and validated against more precise body-composition measurement methods (like hydrostatic weighing) across a large sample, and for most people it produces a reasonably close estimate using just a tape measure — no specialized equipment required, unlike calipers (which need training to use consistently) or DEXA scans (which require clinical equipment). The tradeoff is precision: circumference-based methods have a wider margin of error than clinical-grade methods, and accuracy depends heavily on measuring at the exact correct anatomical landmarks with consistent technique — small measurement errors in exactly where the tape is placed produce meaningfully different body fat percentage estimates.
A worked example
The same person measured by two different people, or by the same person on two different occasions with slightly different tape placement, can get body fat percentage estimates that differ by a few percentage points purely from measurement inconsistency — which is why tracking the trend over repeated consistent measurements (same person, same technique, same landmarks) is more meaningful than treating any single measurement as a precise, one-time clinical result.
How this connects to your other health calculations
Body fat percentage gives a more direct picture of body composition than BMI alone, since BMI can't distinguish muscle mass from fat mass — someone with high muscle mass can have an "overweight" BMI while actually having low body fat, which is exactly the gap this calculator is meant to help clarify. For assessing frame size, which affects how to interpret a given weight or measurement set, the Frame Size Calculator is a related but separate measurement.
Common mistakes
Measuring at inconsistent or incorrect anatomical landmarks — the waist measurement point in particular is easy to get wrong, since "waist" in casual use and the exact anatomical measurement point the formula expects aren't always the same location — is the most common source of an inaccurate estimate; following a precise measurement guide for each landmark, rather than estimating by eye, materially improves accuracy.