How this instrument works
This calculator reproduces the circumference-based body-fat formula the U.S. Navy and Army used as their tape-test standard for four decades. Hodgdon JA and Beckett MB derived it at the Naval Health Research Center in San Diego in 1984, across two reports — 84-11 for men, 84-29 for women — from circumference measurements checked against hydrostatic weighing. Men's percent body fat comes from waist minus neck, adjusted by height; women's equation adds hip circumference, reflecting a fat-distribution pattern different from men's.
Label this clearly as the traditional, historical Army and Navy circumference method, the standard from 1984 through 2024. Army Directive 2023-11 replaced this multi-site (neck, waist, and, for women, hip) approach with a new one-site abdominal-circumference method, phased in starting mid-2024. Defense Department guidance issued in January 2026 moved the Army further still, retiring circumference-based body-fat tape testing altogether in favor of a waist-to-height ratio standard. This page calculates the original 1984 formula accurately; it does not represent current Army policy.
Even at its peak use, the method was an estimate, not a body-composition scan. It correlated well with underwater weighing in the Navy's original validation sample, but circumference readings are sensitive to exactly where and how snugly the tape sits, and the formula was built on a military population that may not resemble every person reading this page. Treat any result here as a historical-method figure, useful for understanding how the old tape test worked, not as a current fitness or health standard.
- Set Sex — the formula shape differs beyond a constant: men's equation uses waist and neck only, women's adds hip.
- Enter Neck circumference (neck), measured just below the larynx, in inches or centimetres.
- Enter Waist circumference (waist) at the navel; the check requires waist to exceed neck.
- If Sex is set to female, enter Hip circumference (hip) at its widest point; this field is unused for men.
- Enter Height (h), then read Estimated body fat (bfPct) as a percentage.
Worked example — three tape-test readings
A man with a 15 in neck, 34 in waist, and 70 in height: waist minus neck is 19 in. log₁₀(19) ≈ 1.2788, times 86.01 gives about 109.99. log₁₀(70) ≈ 1.8451, times 70.04 gives about 129.23, subtracted. Add the constant 36.76 and the estimate lands at about 17.51% body fat — the reference value for this reading.
A woman with a 12 in neck, 30 in waist, 38 in hip, and 65 in height: waist plus hip minus neck is 56 in. log₁₀(56) ≈ 1.7482, times 163.2 gives about 285.31. log₁₀(65) ≈ 1.8129, times 97.68 gives about 177.09, subtracted, then 78.39 subtracted again, for an estimate of about 29.83% body fat.
A taller, leaner-framed man — 16 in neck, 32 in waist, 72 in height: waist minus neck is only 16 in, smaller than the first man's 19 in gap, and height is taller at 72 in rather than 70 in. Both effects pull the estimate down: log₁₀(16) ≈ 1.2041 times 86.01 gives about 103.57, log₁₀(72) ≈ 1.8573 times 70.04 gives about 130.09, subtracted, plus 36.76, for a result of about 10.24% body fat, well below the first man's 17.51%, driven by the narrower waist-neck gap and the added height.
Questions
Is this the current U.S. Army body-fat standard?
No — this reproduces the historical circumference formula the Navy and Army used from 1984 through 2024, developed by Hodgdon and Beckett at the Naval Health Research Center. Army Directive 2023-11 replaced it with a one-site abdominal-circumference method starting in 2024, and Defense Department guidance issued in January 2026 moved the Army again, to a waist-to-height ratio standard, retiring circumference-based percent body fat tape testing. Anyone needing a current official reading should check current Army Body Composition Program guidance rather than this page.
Why does the women's formula use hip circumference and the men's doesn't?
Because the 1984 Navy validation studies found men's and women's body fat correlated with circumferences differently. Men's equation needs only waist and neck; women's equation adds hip circumference, reflecting a fat-distribution pattern the original research found meaningfully different from men's at a comparable waist and neck size.
How accurate was the tape-test method against a real body-composition measurement?
Reasonably well correlated with hydrostatic (underwater) weighing in the Navy's original validation sample, but with a real margin of error, commonly cited at several percentage points either way. Circumference readings are sensitive to tape placement and tension, and a formula fit to one population will drift for body types outside that sample.
Why does a smaller waist-neck gap lower the estimated body fat so much?
Because the formula runs on the logarithm of that gap, waist minus neck for men, waist plus hip minus neck for women, so a proportionally smaller gap pulls the whole first term down sharply. Comparing the 19 in gap in the first worked reading against the 16 in gap in the third shows how much of the swing, from 17.51% to 10.24%, comes from that one difference plus a taller height.
Where do the constants in this formula come from?
From Hodgdon JA and Beckett MB, 'Prediction of Percent Body Fat for U.S. Navy Men/Women from Body Circumferences and Height,' Naval Health Research Center Reports 84-11 and 84-29, 1984. The DoD and Army adopted this Navy-derived method for their own circumference-based tape test for decades afterward.
Should I use this result to judge my own fitness or health?
Treat it as a historical-method estimate, not a fitness verdict or a diagnosis. It was built on a military population using tape measurements rather than a body-composition scan, and current Army standards have since moved past it twice, first to a one-site method in 2024, then to a waist-to-height ratio standard in 2026, so a figure from this page describes what the old formula would have returned, not where current policy or your own health stands.
References
- U.S. Army — Body Composition Program adopts waist-to-height ratio (2026)
- Army Directive 2023-11 — Body Fat Assessment (PDF)
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.