Body fat percentage — Navy method

The U.S. Navy body fat formula: how it works

The U.S. Navy circumference method estimates body fat percentage from tape measurements of the neck, waist, and hips (for women), along with height. It was developed and validated by the U.S. Navy for field use — a way to estimate body composition without lab equipment, underwater weighing, or expensive scans. Despite its simplicity, it correlates reasonably well with laboratory methods at typical body fat levels.

How to take accurate measurements

Measurement technique is everything — a half-inch error can shift results by 1–2 percentage points. Follow these protocols:

• Neck: Measure just below the larynx (Adam's apple), keeping the tape horizontal and perpendicular to the spine. Tilt your head slightly forward to relax the muscles. Don't compress the skin.
• Waist (men): Measure at the navel. Breathe normally and measure at the end of a natural exhale. Do not pull in your stomach.
• Waist (women): Measure at the narrowest point — typically 1–2 inches above the navel — not at the navel. This is the most common measurement error in female body fat estimation.
• Hip (women only): Measure at the widest point, typically around the fullest part of the glutes. Keep the tape horizontal.
• Height: Stand straight, heels together, eyes level. Measure without shoes.

Take each measurement twice and average them. Measure in the morning before eating, after using the bathroom, for the most consistent conditions.

The Navy formulas

The equations use common logarithms (log base 10):

• Male: % BF = 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
• Female: % BF = 495 / (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450

Accuracy: how this compares to other methods

Body composition measurement methods, ranked by accuracy:

• DEXA scan: ±1%. The gold standard. Measures bone density, lean mass, and fat mass regionally. Costs $50–$150.
• Hydrostatic weighing: ±1.5–2%. Requires full submersion; available at universities and research facilities.
• Air displacement plethysmography (Bod Pod):±2–3%. Accurate but expensive equipment; found at sports medicine clinics.
• Navy circumference method: ±3–4%. Free and self-administered; good for tracking trends over time.
• Bioelectrical impedance (BIA scales):±3–5%, but highly variable based on hydration, food intake, and time of day. Not ideal for single-point measurements.
• Skinfold calipers: ±3–5% when done correctly by a trained practitioner; ±8%+ when self-administered.

ACE body fat categories

The American Council on Exercise publishes widely used body fat ranges:

• Essential fat — Men: 2–5%, Women: 10–13%. The minimum for physiological function.
• Athlete — Men: 6–13%, Women: 14–20%. Competitive performance range.
• Fitness — Men: 14–17%, Women: 21–24%. Above average; associated with good health markers.
• Acceptable — Men: 18–24%, Women: 25–31%. Normal range; health risks not significantly elevated.
• Obese — Men: 25%+, Women: 32%+. Associated with elevated cardiovascular and metabolic risk.

Body fat vs. aesthetics vs. health

These categories map loosely to health, not aesthetics. Visible abs for men typically appear at 10–13% — within the "athlete" range. Visible abs for women typically appear at 17–20%. But health risks from body fat are most associated with visceral fat (fat around the organs), not subcutaneous fat. Someone at 22% body fat with low visceral fat has a very different metabolic risk profile than someone at 22% with high visceral fat. The Navy method doesn't distinguish between the two — for visceral fat specifically, waist circumference alone is a reasonable proxy (high risk: >40 inches for men, >35 inches for women).