How to measure
- Neck: just below the larynx, sloping slightly downward in front.
- Waist: at the narrowest point (men) or at the navel (women), relaxed and exhaled.
- Hip: at the widest point of the buttocks (women only).
- Keep the tape snug but not compressing; measure twice and use the average.
The formula
The US Navy method converts circumferences into body density, then into body fat percentage (Siri equation):
- 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
Body fat categories (American Council on Exercise)
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average / acceptable | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Tape measurements carry an error margin of roughly ±3–4%, so treat the result as a trend line rather than an exact figure: measure under the same conditions (morning, fasted) and watch the direction of change.