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US Navy Body Fat Method

The US Navy method uses official circumference equations developed by Hodgdon & Beckett to estimate body fat from tape measurements.[1] It's fast, repeatable, and useful for trends when performed consistently.

You can calculate your current body fat on this site with our Body Fat Calculator. Keep it open while you follow the guide below.

Follow the steps and enter your measurements in the calculator to see your percentage instantly.

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Official Navy formulas (log base 10)

These are the log10 equations published in Navy regulations and derived from Hodgdon & Beckett's research.[1]

All measurements in centimeters (cm). The calculator accepts both metric and imperial; it converts internally.

Men:

BF% = 86.010 · log10(waist − neck) − 70.041 · log10(height) + 36.76

Women:

BF% = 163.205 · log10(waist + hip − neck) − 97.684 · log10(height) − 78.387

The calculator applies these formulas directly, so your inputs feed the same method the Navy uses.[1]

Required measurements

Navy procedure defines each measurement site precisely to keep readings consistent.[2]

  • Height — barefoot, standing tall.[2]
  • Neck — just below the larynx with shoulders relaxed; tape slightly angled downward to the front.[2]
  • Waist (men) — horizontal at the level of the navel after a normal exhale.[2]
  • Waist (women) — narrowest point of the torso between sternum and navel, measured after exhale.[2]
  • Hips (women) — widest point of the buttocks on a level plane.[2]
Technique checklist
  • Use a non-stretch tape on bare skin, keep it horizontal, snug but not compressing tissue.[2]
  • Record each site at the end of a normal exhalation without sucking in or expanding.[2][3]
  • Take two readings (three if they differ by more than 0.5 in / 1.3 cm) and average them.[2]
  • Keep posture neutral: stand tall, shoulders relaxed, head straight ahead during neck and waist checks.[2]
  • Measure under consistent conditions—same operator, time of day, and clothing—to reduce variation.[2][8]

Step-by-step

  1. Switch to your preferred units in the Calculator.
  2. Measure height, then neck, then waist (and hips for women) as described above.
  3. Enter values and review your body fat estimate and BMI side-by-side.
  4. Save measurements (if signed in) to build a trend over time.

Worked example

Male example (metric): height 180 cm, neck 40 cm, waist 85 cm.

Compute Δ = waist − neck = 45 cm.

BF% ≈ 86.010·log10(45) − 70.041·log10(180) + 36.76 → result ≈ 15–17% (approx.).

Your result may vary a bit due to rounding, tape placement, and posture. Use the app's output as your source of truth.

Accuracy vs. lab methods

Validation studies show the Navy equations closely track laboratory methods when technique is consistent.[4][5][6]

  • Potter et al. (2022) observed average bias of −2.6% for men and +2.3% for women compared with DEXA, with ~3–4% standard deviation.[5]
  • Combest et al. (2017) reported intraclass correlations of 0.72–0.83 versus DEXA and ~2–3% mean differences in biased subgroups.[6]

Hodgdon's Navy cross-validations cite standard errors around 3.6–3.8% body fat—similar to other field equations.[4]

Tracking progress

Because the method relies on simple tape sites, it is quick to repeat and highlights changes in girths over time.[2]

Hodgdon concluded the equations' error is comparable to other anthropometric methods, making them practical for monitoring body composition in the field.[4]

Limitations to watch

Small shifts in tape placement, posture, or hydration can change girths and swing the result by a few percentage points.[3][7][8]

Common pitfalls
  • Measuring over clothing, flexing, or tilting the tape changes circumference readings and inflates error.[2][7][8]
  • Switching measurement levels (navel vs. iliac crest, different hip height) yields different waist values.[7]
  • Pulling the tape too tight or too loose—or exhaling inconsistently—shifts the log10 inputs.[2][3]
  • Comparing readings taken at different times of day, hydration levels, or with different operators adds noise.[2][8]

When to use something else If you need clinical-level precision or physique competition prep, consider DEXA or multi-frequency BIA—their 1–2% error requires specialized equipment but delivers more detail.[3][8]

How it compares to other methods

  • DEXA provides regional fat data with ~1–2% error but is expensive and not portable.[8]
  • Skinfold calipers perform similarly when technicians are trained, yet require multiple pinch sites and more skill.[4]
  • BIA devices can be slightly more accurate in some studies but are highly sensitive to hydration and calibration.[3][5]

The Navy favors the tape test because it is low-cost, rapid, and easy to teach for field readiness assessments.[4][8]

FAQ

Do I need hips as a male? No—hips are only used in the women's formula.

Can I use inches? Yes. Choose imperial units in the calculator; conversions happen automatically.

Why did my % change today? Hydration, meal timing, and tape placement shift girths slightly. Track weekly trends.

References

  1. Kelly, Medicine LibreTexts (2025). "The U.S. Navy body fat estimation formula."
  2. Department of the Navy (2023). "Guide 4: Body Composition Assessment (BCA)."
  3. Rodríguez-Sánchez B. et al. (2019). "Body composition techniques."
  4. Hodgdon J. (1990). "Body Composition in the Military Services: Standards and Methods."
  5. Potter M.N. et al. (2022). "Circumference-based predictions of body fat revisited."
  6. Combest T. et al. (2017). "Comparison of circumference body composition measurements and bioelectrical impedance to DEXA."
  7. Mason C. & Katzmarzyk P. (2009). "Variability in waist circumference measurements by anatomic site."
  8. Human Performance Resources by CHAMP. "How the military measures body composition."

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