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The U.S. Navy Body Fat Method
This calculator uses the Hodgdon-Beckett circumference formula, developed at the Naval Health Research Center in 1984 and still used in the U.S. Navy's fitness assessments today. It estimates body fat percentage from a few tape measurements rather than requiring calipers or specialized equipment — validated to within roughly ±3–4% of hydrostatic (underwater) weighing, a laboratory reference method.
All measurements in inches. The logarithms account for the fact that circumference and body fat don't scale in a straight line — an extra inch of waist represents a different amount of fat at a low body fat percentage than at a high one.
Worked Example
Example (male): height 70", neck 15", waist 34"
Applying the formula gives a result of approximately 11.1% body fat.
Example (female): height 64", neck 12", waist 34", hip 42"
Applying the formula gives a result of approximately 15.8% body fat.
How to Measure Accurately
| Measurement | How to take it |
|---|---|
| Neck | Just below the larynx (Adam's apple), tape sloping slightly downward in front |
| Waist (men) | Horizontal, at the navel, after a normal exhale — don't suck in |
| Waist (women) | Horizontal, at the narrowest point of the torso |
| Hip (women only) | Horizontal, at the widest point of the hips/glutes |
How accurate is this compared to a DEXA scan or caliper test?
Less precise than lab methods like DEXA scans, but reasonably close for a tape-measure method — generally cited within about ±3–4% of hydrostatic weighing. It's most useful for tracking trends over time using a consistent measuring technique, rather than as a single precise clinical figure.
Why does the formula use log₁₀ instead of a simple ratio?
Body fat and circumference don't have a straight-line relationship — the formula's log-based structure was derived from regression analysis comparing circumference measurements against underwater-weighing results in a large sample of military personnel, and better fits the real, non-linear relationship than a simple ratio would.
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