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.