How the Navy method works
The U.S. Navy uses circumference measurements to estimate body fat for its fitness standards. Your waist relative to your neck (and hips, for women) is a decent proxy for how much of your weight is fat. Measurements are in centimetres:
Men: %BF = 495 / (1.0324 − 0.19077·log10(waist − neck) + 0.15456·log10(height)) − 450
Women: %BF = 495 / (1.29579 − 0.35004·log10(waist + hip − neck) + 0.22100·log10(height)) − 450
Compared with DEXA scans it is typically within about 3–4 percentage points for most people. It's less accurate for very muscular or very lean bodies. Its real strength is tracking change: measure the same way, same time of day, every 2–4 weeks.
Body fat categories
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obese | 32%+ | 25%+ |
Categories from the American Council on Exercise (ACE).