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US Navy tape-measure estimate
Three tape readings — the method the Navy uses for its own sailors.
HEALTH · BODY COMPOSITION
Body Fat Percentage Calculator: US Navy Method
You need a tape measure, not a lab. The U.S. Navy circumference method — the Hodgdon–Beckett equations from 1984, validated against underwater weighing (r = 0.90) — estimates body fat from three tape readings. Default man: 70 in tall, 15.5 in neck, 34 in waist → 16.52% (Fitness), 31.38 lb of fat. The second panel cross-checks with the Deurenberg BMI formula (24.56% for the same man — the two methods disagree on purpose). Below: where the tape goes, the ACE categories, and the honest ±3.5-point error bar every calculator owes you.
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Deurenberg BMI cross-check
A second, independent estimate from BMI, age and sex — see how they compare.
The 60-second rule
The Navy method is the best $5 body-fat test ever invented — and it is still an estimate. A 70-inch man with a 15.5-inch neck and a 34-inch waist reads 16.52% (Fitness), carrying about 31.38 lb of fat. The same man’s Deurenberg BMI formula says 24.56% — the gap is normal: the Navy method measures where you store fat; Deurenberg guesses from BMI. Trust the trend over months, not one reading, and remember the error bar: ±3.5 points for men, ±3.6 for women.
Where the tape actually goes
This is where Navy estimates live or die. Height: barefoot, back straight. Neck: just below the larynx, tape level, snug but not denting the skin. Waist (men): around the navel, horizontal — do not suck in. Waist (women): the narrowest point of the abdomen. Hips (women only): the widest point of the buttocks. Measure against bare skin, take each reading three times and average, and re-measure under the same conditions each time.
The worked example, line by line
Navy, default man: %BF = 86.010 × log10(34 − 15.5) − 70.041 × log10(70) + 36.76 = 86.010 × 1.2672 − 70.041 × 1.8451 + 36.76 = 16.52%. Fat mass: 190 × 0.16517 = 31.38 lb; lean mass: 190 − 31.38 = 158.62 lb.
Deurenberg, same man: BMI = 27.26; %BF = 1.20 × 27.26 + 0.23 × 35 − 10.8 − 5.4 = 24.56%. The 8-point gap is expected: BMI cannot see that a 190-lb frame at 27.26 BMI can be lean or soft — the Navy equation can.
ACE body-fat categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Population-level descriptive ranges (American Council on Exercise); healthy ranges rise somewhat with age.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Navy body fat % (men) | 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76 | 16.52% at the defaults — Fitness for a man (Hodgdon–Beckett, inches, base-10 log). |
| Navy body fat % (women) | 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387 | 26.59% for 64/13/28/38 — Average for a woman; hip accounts for female distribution. |
| Fat / lean mass | weight × %BF; weight − fat mass | 31.38 lb fat, 158.62 lb lean at the defaults — the number that should move over time. |
| Deurenberg % | 1.20 × BMI + 0.23 × age − 10.8 × sex(1=m) − 5.4 | 24.56% at the defaults — a rough population estimate for comparison only. |
Who uses this
- Cutting / bulking lifters: tracking whether the scale change is fat or muscle over a training block.
- New exercisers: a baseline number that moves before the mirror does.
- Military and first-responder candidates: checking against body-composition screening standards.
- Trend trackers: same tape, same spots, monthly — the slope is the product, not the point.
Accuracy & limitations
The Hodgdon–Beckett equations were fit to 602 men and 135 women in the U.S. Navy and validated against hydrostatic weighing: correlation r = 0.90 (men) and 0.85 (women), standard error about ±3.5 and ±3.6 percentage points — so 16.52% really means roughly 13–20%. It fails systematically for very muscular people (reads high) and older adults with muscle loss (reads low). It is an estimate of composition, not a diagnosis; for medical decisions see a clinician. Deurenberg is a population equation — expect it to read high for the muscular and low for the sedentary.
Cite this calculatorBright Side Kit. “Body Fat Calculator: US Navy Method.” brightoolbox.com, 2026.
Bright Side Kit. "Body Fat Calculator: US Navy Method." https://brightoolbox.com/body-fat-percentage-calculator/ Accessed October 23, 2026.Frequently asked questions
How accurate is the US Navy body fat method?
For a field method, very good: the equations were validated against underwater weighing with correlation r = 0.90 for men and 0.85 for women. The standard error is about ±3.5 percentage points (men) and ±3.6 (women). So a 16.52% reading really means roughly 13–20% — use it for trends, not single readings.
Why does the Navy formula use neck size?
The neck is a proxy for lean mass: a thicker neck (relative to the waist) signals more upper-body muscle, which the logarithmic equation converts into a lower body-fat estimate. It is also why the formula subtracts neck from waist — the equation is really comparing fat-storage sites against lean-mass sites.
Why does the Navy method disagree with my BMI-based estimate?
Because BMI cannot see composition. A 190-lb, 70-inch man has a BMI of 27.26 (“overweight”), but the Navy tape says 16.52% — Fitness. Deurenberg’s formula (24.56% for the same man) is built from BMI, so it inherits BMI’s blind spot. When the two disagree, the tape is usually the better story.
What is a healthy body fat percentage?
By the American Council on Exercise ranges: men 18–24%, women 25–31% is “average”; 14–17% / 21–24% is “fitness”; 6–13% / 14–20% is “athletes”. Essential fat — the minimum for basic function — is 2–5% for men, 10–13% for women. Healthy ranges rise somewhat with age.
Do I measure the waist at the navel or the narrowest point?
Men: at the navel, level. Women: at the narrowest point of the abdomen. This follows the Navy protocol the equations were fitted on — measuring anywhere else (sucking in, tape at an angle, over clothing) silently moves the result. Three readings, average them, same conditions each time.
Is the Navy method better than calipers?
For most people, yes in practice: calipers need trained hands and the same pinch sites every time, while a tape is harder to do wrong. Both estimate with about ±3–4 points of error versus lab methods like DXA. The winner is whichever you will do consistently — monthly, same spots, same conditions.