Body fat percentage
The US Navy tape method, plus lean mass and fat mass.
A rough estimate; tape methods carry several points of error.
Fitness
Muscle, bone, organs, water
Under 0.5 is the usual target
Reference ranges
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25%+ | 32%+ |
How it works
The US Navy method estimates body fat from circumference measurements and height. It works because fat distributes predictably enough across a population that waist girth relative to neck and height correlates with total fat.
Men: %fat = 495 / (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450
Women: %fat = 495 / (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.221·log₁₀(height)) − 450 How accurate is it?
Validation studies put the standard error at roughly 3–4 percentage points against hydrostatic weighing. That is good enough to track a direction over months, and not good enough to argue about a single point. DEXA is the practical gold standard; skinfold calipers in trained hands sit somewhere between.
Measure consistently, not perfectly
The number matters less than the trend. Measure at the same time of day, in the same state of hydration, with the same tape, and compare month to month. A one-point move week to week is measurement noise.
Essential fat is not optional
Below about 5% for men and 12% for women, the body is drawing on fat that organs and hormones require. Sustained very low body fat disrupts endocrine function — in women it commonly stops menstruation, a recognised marker of energy deficiency, not of fitness.
Sources
Hodgdon JA, Beckett MB, “Prediction of percent body fat for U.S. Navy men and women from body circumferences and height”, Naval Health Research Center, 1984. Category ranges follow the American Council on Exercise.