How this works
The US Navy circumference method estimates body fat from a few simple measurements: height, neck circumference, waist circumference, and (for women) hip circumference. It was published in 1984 by Hodgdon and Beckett at the Naval Health Research Center after validating the formula against hydrostatic weighing. It's less precise than DEXA or hydrostatic methods but accurate within ~3 % for most adults — and you don't need calipers, just a flexible tape measure.
The formula
Take measurements with a flexible (non-stretchable) tape, snug but not compressing. Neck: just below the larynx, sloping down toward the front. Waist: at the navel for men, at the narrowest point for women. Hip: at the widest point of the buttocks. The result has built-in classification ranges (essential / athlete / fitness / average / obese) which differ by sex.
Example calculation
- A man, 178 cm tall, neck 38 cm, waist 85 cm.
- log10(85 − 38) = log10(47) ≈ 1.672. log10(178) ≈ 2.250.
- BF% = 86.010 × 1.672 − 70.041 × 2.250 + 36.76 ≈ 14.4 % — within the "fitness" range for men.
- At weight 80 kg → fat mass ≈ 11.5 kg, lean mass ≈ 68.5 kg.
Frequently asked questions
How accurate is the US Navy method?
Within about ±3 % of hydrostatic weighing for typical adults, which is good enough for tracking trends month-to-month. It's less reliable at the extremes — very lean athletes can come out a few points high (the formula assumes a "typical" relationship between waist size and body fat that gets weaker the more developed you are abdominally), and significantly overweight individuals can come out a few points low. DEXA scans are more accurate but cost £100+ a session.
Where exactly do I measure neck, waist, and hip?
Neck: just below the larynx ("Adam's apple"), tape sloping slightly down toward the front. Waist: at the navel for men, at the narrowest part of the torso (typically just above the belly button) for women. Hip: at the widest horizontal point of the buttocks. Take all measurements at the end of a normal exhale, tape snug but not compressing skin.
Why does the female formula need an extra measurement?
Body fat distribution differs between sexes — men tend to store fat predominantly around the waist, women predominantly around the hips and thighs. The waist-only formula calibrated against male data wouldn't accurately predict total body fat for women, so the original 1984 paper added the hip measurement and refit the coefficients separately. The same principle is why the male and female classification ranges differ by ~5-7 percentage points across all categories.