Body Fat Calculator — US Navy Method
No lab needed: a tape measure around your neck, waist (and hips for women) plus your height gives a body-fat estimate within a few points of a lab scan.
How it works
Body density (Hodgdon & Beckett, measurements in cm), then the Siri conversion BF% = 495 ÷ density − 450. Men: density = 1.0324 − 0.19077·log10(waist − neck) + 0.15456·log10(height). Women: density = 1.29579 − 0.35004·log10(waist + hip − neck) + 0.22100·log10(height).
Examples: man, 180 cm, waist 90 cm, neck 38 cm: density 1.0536, body fat 19.8% (Average). Woman, 165 cm, waist 75 cm, hips 98 cm, neck 32 cm: about 29.0% (Average).
Frequently asked questions
How accurate is the tape method?
Typically within 3–4 percentage points of DEXA for most people. Tape placement and posture move the number, so track the trend, not a single reading.
Where exactly do I measure?
Neck just below the Adam's apple, waist at the navel (relaxed, end of exhale), hips at the widest point, feet together. Keep the tape level, not angled.
Why do women need hips?
Because fat distributes differently: hips capture lower-body fat that the waist alone misses, which is why the women's equation has its own constants.
Is this the Navy's current test?
Not anymore: from January 2026 the Navy screens by waist-to-height ratio first. The classic circumference equations are still widely used as a civilian estimate.