Body Fat Calculator U.S. Navy 1984
Estimate body fat with just a tape measure — Navy formula + CUN-BAE comparison + ACE classification + fat and lean mass.
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⚠️ This estimate uses the Navy tape-measure formula and does not replace medical diagnosis, BIA, or DEXA. Standard error vs. gold-standard methods is ±3–5%. Accuracy is lower for pregnancy, extreme muscle mass (bodybuilders, severe underweight), and adolescents (under 19). For accurate body composition, consider DEXA or hydrostatic weighing.
Navy Formula (1984)
| Sex | Formula (inches) |
|---|---|
| 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 |
cm inputs are converted to inches (÷ 2.54) automatically.
CUN-BAE Formula (Gómez-Ambrosi 2012)
Validated by the University of Navarra Hospital (Spain), based on BMI, age, and sex. More accurate than Navy in obese populations. This calculator displays both for comparison:
| Variable | Meaning |
|---|---|
| BMI | weight (kg) ÷ height (m)² |
| age | chronological age |
| sex | 0 = male / 1 = female |
If the two formulas differ by more than ±5 percentage points, suspect a measurement error. Re-measure in the same posture, in the morning on an empty stomach.
ACE Body Fat Classification (reference)
| Category | Men | Women | Description |
|---|---|---|---|
| Essential fat | 2–5% | 10–13% | Minimum for life — below: hormonal / immune issues |
| Athletes | 6–13% | 14–20% | Optimal performance — hard to reach for most |
| Fitness | 14–17% | 21–24% | Optimal metabolic health |
| Average | 18–24% | 25–31% | Most adults fall here |
| Obese | 25%+ | 32%+ | Elevated metabolic and cardiovascular risk |
Women have 5–9 percentage points more essential fat due to estrogen and reproductive function. Significant changes occur after pregnancy and menopause.
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Frequently Asked Questions
How accurate is the Navy formula?
The U.S. Navy adopted this tape-measure formula in 1984. Compared with hydrostatic weighing
(the historical gold standard), average error is ±3–4%. Less precise than DEXA or BIA, but the
most common method that requires only a tape measure. This calculator also displays the BMI-based
CUN-BAE (Spain 2012) value — large discrepancies between the two suggest a measurement error.
How do I take the measurements?
Neck: just below the larynx (Adam's apple), at the narrowest part, with the tape level.
Waist: men measure at the navel; women measure at the narrowest point (usually 2–3 cm above the navel).
Hips (women only): the widest point around the buttocks.
Breathe out naturally during measurement; the tape should rest lightly on the skin without compressing it.
Measure in the morning on an empty stomach, in the same posture, and average several attempts.
What classification does this calculator use?
American Council on Exercise (ACE) standards — Men: essential 2–5%, athletes 6–13%,
fitness 14–17%, average 18–24%, obese 25%+. Women: essential 10–13%, athletes 14–20%,
fitness 21–24%, average 25–31%, obese 32%+. Women naturally maintain 5–9 percentage points
more body fat than men due to hormonal and reproductive function.
BMI vs body fat — which is more accurate?
Body fat percentage is more accurate. BMI only considers height and weight, so muscular
athletes can be misclassified as obese, and 'skinny fat' (normal BMI but body fat 30%+)
is missed. BMI is still useful as a quick screen because it requires no tape measure.
If you train regularly or have an atypical build, evaluate yourself using body fat percentage instead.
Why do Navy and BIA / scale results differ?
The two methods measure different things. Navy uses circumference regression (shape
estimation); BIA scales use bioelectrical impedance to estimate water content, then convert
to body fat. BIA is sensitive to hydration (fasting, exercise, menstruation) and can vary ±2–3%
in the same person. Both methods have a ±3–5% standard error — focus on trends rather than
absolute values. Gold standards are DEXA and hydrostatic weighing (±1%).
How do I lower my body fat?
Preserve muscle while losing fat: ① calorie deficit (0.5–1 kg/week, TDEE − 500 kcal),
② protein 1.6–2.2 g/kg/day (Morton 2018, BJSM), ③ resistance training 3+ days/week
(prevents muscle loss), ④ adequate sleep (7+ hours) to normalize cortisol, leptin, testosterone.
Cuts faster than 1 kg/week often cause muscle loss, and body fat percentage may not actually drop.
References
Last reviewed: 2026-05-10
- Navy formula — Hodgdon JA, Beckett MB. "Prediction of percent body fat for U.S. Navy men/women from body circumferences and height." Naval Health Research Center Report No. 84-11/29, 1984
- CUN-BAE — Gómez-Ambrosi J et al. "Body mass index classification misses subjects with increased cardiometabolic risk factors related to elevated adiposity." Int J Obes 2012;36(2):286-94
- Body fat classification — American Council on Exercise (ACE), Body Composition Standards (Lee & Nieman 2013, Nutritional Assessment 6th ed.)
- Cutting and muscle preservation — Morton RW et al. BJSM 2018
- Method accuracy comparison — Kuriyan R. "Body composition techniques." Indian J Med Res 2018;148(5):648-658