How it works
The US Navy circumference method estimates body fat from tape measurements — no calipers or DEXA required. Measurements are converted to inches inside the engine, then run through the published DoD formulas. For men: BF% = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women, hip enters the waist+hip−neck term with a different coefficient set. Worked example — male, 178 cm height, 85 cm waist, 38 cm neck: after conversion to inches the formula returns about 10.1% body fat, labelled Athletic on common fitness bands (essential ≈2–5%, athletes 6–13%, fitness 14–17%, average 18–24% for men). Accuracy is typically ±3–4% versus hydrostatic weighing — useful for tracking trends when you measure the same way each time. Measure waist at the navel after a normal exhale, neck below the larynx with the tape horizontal, and hips at the widest point for women. Hydration and a large meal can shift girth slightly, so compare morning-to-morning readings rather than post-dinner ones. This is an estimate for fitness planning, not a medical diagnosis.
Formula
Men (inches): BF% = 495/(1.0324 − 0.19077×log10(waist−neck) + 0.15456×log10(height)) − 450 | Women: hip included in log term
Tips
- Measure at the same time of day — waist expands after meals and shrinks after dehydration.
- Tape parallel to the floor; snug contact, not compressing skin.
- Track monthly trends rather than obsessing over a single reading's absolute value.
- Women must include hip measurement — the male formula omits it deliberately.
Frequently asked questions
- How accurate is the Navy body fat method?
- Typically within ±3–4% of hydrostatic weighing when measurements are taken correctly. Consistent technique matters more than the formula choice for tracking progress.
- What does the default male example return?
- About 10.1% body fat (Athletic category) for 178 cm height, 85 cm waist and 38 cm neck.
- Where do I measure waist for Navy formula?
- At the navel (belly button), relaxed standing, after a normal exhale — not sucked in, not fully expanded.
- Why is hip required for women?
- Female fat distribution includes hips and thighs; the Navy female equation adds hip circumference inside the log term to avoid underestimating total body fat.