The Navy method is accurate within ±3-4% for most people compared to hydrostatic weighing. It tends to underestimate body fat in very lean individuals and overestimate in obese individuals. For tracking trends over time, it is reliably consistent.

Measure your neck circumference just below the larynx (Adam's apple) with the tape sloping slightly downward at the front. Stand straight, look forward, and keep the tape snug without compressing the skin. Measure to the nearest half inch.

Neck circumference serves as a proxy for overall frame size and lean mass. A thicker neck relative to waist measurement indicates more muscle mass. The formula uses the difference between waist and neck to estimate the ratio of fat to lean tissue.