Navy Body Fat Calculator
Estimate body fat % from a few tape-measure inputs using the U.S. Navy method.
How We Calculate This
This uses the U.S. Navy circumference method, developed by the Naval Health Research Center from a few tape-measure inputs (height, neck, waist, and — for women — hip) instead of specialized equipment. The formula relies on base-10 logarithms (log₁₀), not natural log — mixing the two up is the most common manual calculation error.
In the original validation against underwater (hydrostatic) weighing, it correlated at roughly r=0.90 for men and r=0.85 for women, with a typical error margin of about 3–4 percentage points — a solid estimate, not a clinical-grade measurement. It's also less reliable at the extremes of body composition, e.g. very high muscle mass or very low body fat, where circumference alone tracks fat mass less well.
Where you place the tape matters more than most people expect. Measure your neck just below the larynx (Adam's apple), and your waist at the navel — the same spot in both cases regardless of where your pants sit. For the hip measurement (women only), measure at the widest point around the hips and glutes. The tape should sit snug against the skin, not compressing it — pulled too tight, it reads smaller than your true circumference and understates your result. Because the formula is sensitive to exact placement, the most useful thing you can do isn't a single perfect reading — it's measuring the same spot, the same way, every time. That consistency is what makes the trend over weeks meaningful, even if any one reading is off by a bit.
Read the validation data →