How the Navy body fat calculator works
How the Navy method works
Fat distributes predictably: waist grows with fat while neck stays relatively constant. The formula compares log-scaled circumference ratios against height to estimate density, then converts to fat percentage. It was validated against hydrostatic weighing across thousands of service members — and adopted because a tape measure deploys onto an aircraft carrier.
Accuracy: honest numbers
Against DEXA and hydrostatic weighing, the Navy method runs within 3–4% for most people, with individual errors occasionally larger (unusual fat distribution, very muscular builds). Its real superpower is precision-by-consistency: repeated under the same conditions, it detects 1–2% changes reliably — which is exactly what tracking needs.
Measurement hygiene
Same time of day (morning, post-bathroom), tape horizontal and snug-not-compressing, relaxed posture, no sucking in. Neck below the larynx, waist at the navel (not the pants line), hips at the widest point for women. Two or three repeats, averaged. Bad measurements produce confident nonsense — the method deserves five careful minutes.