US Navy Body Fat Formula & Calculator
Estimates body fat from a tape measure — neck, waist and height (women also add hip). The most widely used tape method in the world, because it needs no equipment.
The US Navy formula (Hodgdon–Beckett, 1984) turns body circumferences into a body-fat estimate using logarithms. It correlates about 0.90 with hydrostatic weighing and lands within roughly ±3–4 percentage points — accurate enough to track your trend, not to treat as an exact number. It is one of several methods WIMSTA runs at once.
US Navy and RFM disagree by 4.3 pp on the same tape. The full calculator adds Deurenberg, CUN-BAE and Covert Bailey — a range, not one number.
Getting the tape placement right matters here → How to measure your waist and abdomen
Inches vs centimetres — the constant that trips people up
Because the formula is fitted with logarithms, its numeric constants depend on the unit the measurements are in. There is a centimetre form (shown above) and a separate inches form with different constants — and copying one while feeding it the other unit is a classic bug you'll find on many calculator sites. WIMSTA uses the centimetre form end-to-end, converting your input if you switch units, so the two can never be mixed.
Women use a different equation again — waist plus hip minus neck, with its own constants — because hip circumference carries information the male equation doesn't need.
Accurate for
Adults of ordinary build measuring carefully. Error ≈ ±3.5 pp (SEE), r ≈ 0.90.
Off for
Very lean or very heavy builds, and anyone who measures the waist in the wrong place. Not valid in pregnancy or for under-18s.
One formula is a decision. See the range.
On the same tape, the US Navy formula and RFM can differ by several points — and Deurenberg, CUN-BAE and Covert Bailey add more. The calculator shows the honest range they agree on.
Open the body-fat calculatorHodgdon & Beckett (1984). U.S. Navy NHRC Reports 84-11 / 84-29 (DTIC ADA143890 / ADA146456). Derived on U.S. military personnel and validated against hydrostatic weighing — n = 594, R = 0.903, SEE = 3.52 pp for men; n = 202, R = 0.856, SEE = 3.61 pp for women. These NHRC reports are the primary derivation of the method — a U.S. government technical report, cited by its DTIC accession number (the stable identifier), not a peer-reviewed journal with a DOI. That is why we mark it ✅ primary and still say plainly what kind of source it is.
We also checked our own maths. WIMSTA computes the centimetre (density → Siri) form; the modern direct-% form is fixed in Hodgdon & Friedl (1999, DTIC ADA370158). These are two parameterisations of the same method and agree to within ~0.1–0.3 percentage points — we verified ours coefficient-by-coefficient against the primary source, so the constants can’t drift or mix inch/centimetre units.
Spot an error in this formula? Report it →
FAQ
How accurate is the US Navy body fat formula?
It was validated against hydrostatic weighing in military personnel with a correlation around 0.90 and a typical error of ±3–4 percentage points. That is good for tracking your own trend over weeks, less so for comparing one person to another or to a lab scan.
What measurements do I need?
Neck, waist and height for men; women also add hip. Measure with a flexible tape on bare skin, relaxed, and take each measurement twice — the tape angle at the neck and where you read the waist change the result more than real fat does.
Why do inches and centimetres give different constants?
The formula is a curve fitted with logarithms, so the numeric constants depend on the unit the inputs are in. There is a centimetre form and an inches form, and mixing them up is a classic copy-paste bug on other sites. This calculator uses the centimetre form throughout.
Is the US Navy formula better than BMI?
For estimating body fat specifically, yes — it uses where your weight sits, not just how much. But it is still one tape-based estimate. The honest read is to run several formulas and look at the range they agree on.
See how every method is sourced on the method page.