Body Fat Calculator (US Navy Method)
A tape measure and three measurements estimate your body fat percentage — the same method the U.S. military uses for fitness screening.
Neck: measure below the larynx, tape sloping slightly down at front. Waist: at navel for men; at the narrowest point for women. Keep the tape snug, not tight.
How the math works
women: %BF = 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.221·log₁₀(height)) − 450
This is the circumference-based estimator adopted by the U.S. Navy: because fat accumulates in predictable places (belly and neck relative to frame for men; hips, thighs and waist for women), a few tape measurements carry real information. It's typically within 3–4 percentage points of DEXA scans — less precise than a lab, far cheaper than one, and its real power is trend-tracking: measure the same way weekly and the direction is trustworthy even when the absolute number wobbles.
Body fat categories (ACE)
| 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%+ |
FAQ
- Why do I need hip measurements as a woman?
- Women store fat preferentially in hips and thighs, so the formula needs all three circumferences to separate fat from frame.
- Can body fat be too low?
- Yes — below essential fat (2–5% men, 10–13% women) hormones, immunity and bone health suffer. Leaner is not better past a point.
- How often should I re-measure?
- Every 2–4 weeks under identical conditions (morning, before eating). Daily readings just reflect water and food, not fat.
This tool provides general information only and is not medical advice. Talk to a qualified healthcare professional about your health and body composition.