Body Fat Calculator (US Navy method)
Measure your neck and waist (plus hip for women), enter your height, and the 1984 US Navy circumference formula gives a body-fat estimate without scales or DEXA scans. Accurate to roughly ±3–4 %.
Please enter a valid number
Body fat
16.1%
Fitness
Lean body mass (LBM) —
Fat mass —
Range
Regular-exerciser level — generally healthy.
Uses the US Navy circumference formula (Hodgdon & Beckett, 1984), accurate to roughly ±3–4 %. For higher precision (DEXA, BIA) consult a medical professional.
Formula
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 All measurements in cm
- · Formula from Hodgdon & Beckett (1984), Naval Health Research Center — still used by the US Department of Defense for body composition screening.
- · Neck: narrowest point just below the larynx. Waist: at the navel for men, narrowest part of the abdomen for women. Hip: widest point of the hips.
- · ACE / ACSM body-fat ranges (adults) — Men: essential 2–5 %, athletic 6–13 %, fitness 14–17 %, average 18–24 %, obese ≥ 25 %.
- · Women carry more essential fat — essential 10–13 %, athletic 14–20 %, fitness 21–24 %, average 25–31 %, obese ≥ 32 %.
- · Lean body mass (LBM) = weight × (1 − BF %). Useful as a baseline to preserve muscle while cutting fat.
- · Not suitable for pregnant women, competitive bodybuilders (very low body fat or unusually thick necks) or anyone under 18. DEXA or hydrostatic weighing remains the gold standard.
Frequently asked
Is the US Navy formula more accurate than a body-fat scale (BIA)?
Both are estimates with similar accuracy (±3–4 %). BIA scales are heavily influenced by hydration, recent meals and exercise, so values jump even on the same day. The Navy circumference method only depends on tape-measure technique, so it tends to be steadier over time. For ±1 % precision you need DEXA or hydrostatic weighing — but for tracking trends, circumference works well.
Should I measure naked or in light clothing?
Measure on bare skin or over very thin clothing — keep the tape touching the skin. Thick clothing can add 1–3 cm of girth, which inflates the body-fat estimate by 2–4 %. Always measure at the same time of day (ideally first thing in the morning, after using the bathroom) to make the comparison meaningful.
I'm muscular or heavily trained — does the result still hold?
It can be off for athletes. The formula assumes a typical neck-to-height ratio; people with thickly muscled necks (long-term lifters) are flagged as leaner than they are, while powerlifter-style midsections are flagged as fatter. Highly trained individuals are better assessed with skinfold callipers or DEXA than with BMI or this formula.
How often should I re-measure?
Every 2–4 weeks is the sweet spot. Body fat changes slowly — a healthy cut runs around 0.25–0.5 % per week — so daily measurements just show tape-measure noise. Measure at the same time of day, same posture and same anatomical landmark each time, then track the trend rather than any single value.
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