Navy Body Fat Formula
The formula
The Navy uses different formulas for men and women, both based on the circumferences of fat-storing sites (waist for both, plus hips for women) offset by the neck (used as a proxy for lean mass).
Men:
BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Women:
BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
All measurements in inches. The calculator above converts automatically if you choose cm.
How accurate?
The Navy formula has a standard error of approximately ±3.5% body fat compared to hydrostatic weighing. It's less accurate than DEXA scans or hydrostatic weighing but vastly more accessible — all you need is a tape measure.
It tends to overestimate for very lean individuals and for those with unusual proportions (e.g. very wide shoulders, large neck for build). Use it for tracking trends rather than as an absolute number.
Sources & standards
This calculator uses the exact Hodgdon–Beckett regression formula from the original 1984 Naval Health Research Center technical reports. Published validation reports a correlation of approximately r=0.90 against hydrostatic (underwater) weighing, with a standard error around 3–4 percentage points — consistent with the ±3.5% figure quoted above. This tool is for personal tracking, not an official military Body Composition Assessment.
- Hodgdon JA, Beckett MB (1984). “Prediction of Percent Body Fat for U.S. Navy Men from Body Circumferences and Height.” Naval Health Research Center, Report No. 84-11 — original derivation of the formula used on this page, via DTIC (U.S. Defense Technical Information Center) source
- Hodgdon JA, Beckett MB (1984). “Prediction of Percent Body Fat for U.S. Navy Women from Body Circumferences and Height.” Naval Health Research Center, Report No. 84-29 — companion report for the female-specific formula
- U.S. Navy Physical Readiness Program, OPNAVINST 6110.1J — current official instruction governing use of this method within the Navy