Quick answer
Your Navy-method body fat estimate depends on your own neck, waist, height and (for women) hip measurements, so there's no single typical number. In the calculator's own worked examples, a 178 cm man with a 38 cm neck and 85 cm waist comes out to 16.4%, and a 165 cm woman with a 32 cm neck, 75 cm waist and 98 cm hip comes out to 28.9%. The 1984 reports give standard errors of 3.52 points (men) and 3.72 (women) against underwater weighing.
How the Navy method actually works
The US Navy body fat method estimates body fat percentage from three or four tape measurements (neck, waist, height and, for women, hip) instead of calipers, a bioelectrical scale or a DEXA scan. Body fat percentage is the share of body weight that is fat; the men's report calls it the percentage of body weight contributed by fat mass. Hodgdon and Beckett of the Naval Health Research Center published the equations in 1984: report 84-11 for men and report 84-29 for women. Each was found by regression against body density measured by underwater (hydrostatic) weighing. The men's sample was 602 male naval personnel aged 18 to 56 (mean age 31.9), serving ashore and afloat. The women's was 214 female naval personnel aged 18 to 44 (mean age 26.5). The authors considered only circumferences, height, body weight and age, because those are the measures most reliably made in the field by personnel with minimal training; weight and age did not enter either equation. This page applies the 1984 equations. It does not describe what the Navy or any other service uses today, because we did not read their current procedures.
The equations are logarithmic and unit-specific: the coefficients below assume centimetres, which is why this calculator converts imperial inputs internally before running the math. Each predicts body density, and the reports convert density to percent body fat with Siri's (1961) equation, which gives the 495 ÷ … − 450 form shown here:
Women: BF% = 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450
(all measurements in centimetres)
Where exactly to place the tape
These are the sites described in the 1984 reports for the equations on this page; the hip is the one exception, noted in its entry. In the reports the person stood relaxed, the tape conformed to the skin without pressing into it, and, apart from the neck, it was applied in the plane at right angles to the long axis of the body part measured; for the waist and hip of someone standing upright, that is level all the way round. The abdomen was measured at the end of a normal breath out. The everyday words below (voice box, Adam's apple, breastbone, navel, buttocks) are this page's glosses for the reports' anatomical terms.
- Neck (men and women): just below the larynx (the voice box, whose front is the Adam's apple), with the tape sloping slightly downward toward the front.
- Waist, men: level with the navel.
- Waist, women: at the narrowest width of the abdomen, about midway between the lower tip of the breastbone (xiphoid) and the navel. This is above the navel, not at it.
- Hip (women only): at the level of the greatest protrusion of the buttocks (the gluteal muscles). The men's report describes this site; the women's report uses the hip in its equation, but its own list of sites, in the copy we read, has no entry for it.
- Height: standing height, without shoes. The 1984 reports say standing height, with people measured in swimwear or shorts; “without shoes” is how the 2022 Marine study cited below words it.
The 1984 reports measured each site twice, took a third reading if the first two differed by more than 1 cm (about 0.4 inch), and used the mean of the readings at that site. They recorded circumferences to the nearest millimetre and height to the nearest quarter inch. The tape position matters to the result: with this calculator's default male entries (70 in height, 15.5 in neck, 34 in waist) the estimate is 16.5%, and moving the waist to 34.5 in gives 17.4%.
How accurate is it, really?
An equation's standard error is the typical size of its misses, not a limit on them: if the misses follow a normal (bell-shaped) distribution, which the reports do not state, about two estimates in three miss by less than one standard error and about one in three by more. The two 1984 reports give it against underwater weighing, the method the equations were fitted to, and the 1998 study below used underwater weighing too. In the 1984 development samples the tape was in the hands of one of two trained investigators, so those figures do not include any extra error from measuring yourself:
| Sample | Men | Women |
|---|---|---|
| 1984 development sample (the equations were fitted to it) | 3.52 (602 men) | 3.72 (214 women) |
| 1984 cross-validation on separate samples | 2.70 (100 men) | 4.36 (66 Canadian Forces women); 4.04 (80 US Navy women) |
| 1998 sample of Navy and Marine Corps personnel (pure error) | 3.56 (266 men) | 5.04 (239 women) |
The 1998 authors say a pure error is read much like a standard error. The range in the result above is the estimate plus and minus the 1984 development-sample figure for your sex: 3.52 percentage points for men, 3.72 for women. Every later figure for women is larger than 3.72, so for women the range may be narrower than the misses seen in those samples.
Against DXA the picture is different, because DXA is a different reference. A 2022 study of 609 fit US Marines (430 men and 179 women, aged 18 to 57; Potter and colleagues) compared a circumference estimate, made with the Department of Defense's later reformulation of these equations, with DXA scans. On average the circumference estimate was lower than DXA for men and higher for women. For men the difference was −2.6 ± 3.7 percentage points in those aged 30 or under and −2.5 ± 3.7 in those over 30; for women it was +2.3 ± 4.3 and +1.3 ± 4.8 (circumference estimate minus DXA, with the ± figures as the authors print them). On an individual basis, lean men and women were overestimated and people with higher body fat were underestimated. The authors conclude that the method gives the Marine Corps a field expedient way to classify individuals for obesity prevention, but does not provide research-grade quantitative body composition data.
A 2019 study of the Navy's body composition assessment (Latour, Peterson and Riner; we read only its abstract, which does not say who was measured) reports that standalone DXA measurements would increase the estimated body fat of men and decrease that of women compared with the Navy's circumference method as it then stood. That is the direction the Marine study found.
Worked example — male
Height 178 cm (5'10"), neck 38 cm, waist 85 cm, weight 80 kg.
waist − neck = 47 cm. log₁₀(47) = 1.672098, log₁₀(178) = 2.250420.
Denominator = 1.0324 − (0.19077 × 1.672098) + (0.15456 × 2.250420) = 1.0324 − 0.318986 + 0.347825 = 1.061239.
BF% = 495 ÷ 1.061239 − 450 = 466.436 − 450 = 16.436, which rounds to 16.4%.
With the men's standard error of 3.52, the calculator's headline reads 13–20%. At 80 kg, 16.4% body fat splits into roughly 66.9 kg lean mass and 13.1 kg fat mass.
Worked example — female
Height 165 cm, neck 32 cm, waist 75 cm, hip 98 cm, weight 65 kg.
waist + hip − neck = 141 cm. log₁₀(141) = 2.149219, log₁₀(165) = 2.217484.
Denominator = 1.29579 − (0.35004 × 2.149219) + (0.22100 × 2.217484) = 1.29579 − 0.752313 + 0.490064 = 1.033541.
BF% = 495 ÷ 1.033541 − 450 = 478.936 − 450 = 28.936, which rounds to 28.9%.
With the women's standard error of 3.72, the calculator's headline reads 25–33%. At 65 kg, that is about 46.2 kg lean mass and 18.8 kg fat mass.
What ACE is quoted as saying is typical
An excerpt of a Very Well Health article (26 February 2024), posted on the American Council on Exercise's press-room page, says that, according to ACE, a body fat range of 25% to 31% for women, or 18% to 24% for men, is typical for the average non-athlete. The article's next sentence, which names no source, adds that a body fat below 14% for women or 6% for men may be considered dangerously low (ACE press room). That excerpt gives no other ranges, so this calculator does not place your result in a category.
Limitations
The 1984 equations were fitted to samples of naval personnel (602 men aged 18 to 56 and 214 women aged 18 to 44), and the women's report notes that equations of this kind tend to be population specific. They were fitted against underwater weighing, not DXA. In the 2022 Marine study the circumference method read lean people higher, and people with more body fat lower, than DXA did, and the authors conclude it is not suitable for applications requiring quantitative body composition assessment. The number is an estimate with the error shown above.
This tool is for general fitness information only. It is not medical advice, and it does not diagnose or assess health risk. Talk to a qualified professional about your own health.
FAQ
How accurate is the Navy body fat method?
The 1984 reports give a standard error of 3.52 percentage points of body fat for men and 3.72 for women, measured against underwater weighing. Later samples of women gave 4.36, 4.04 and 5.04. Against DXA, a 2022 study of fit US Marines found the circumference method read lower than DXA on average for men (by 2.5 to 2.6 points) and higher for women (by 1.3 to 2.3 points), and the authors print ± figures of 3.7 to 4.8 points alongside those averages. It is an estimate, not a diagnostic or medical measurement.
Where exactly do I measure my neck, waist, and hip?
Neck: just below the larynx (the voice box, whose front is the Adam's apple), with the tape sloping slightly downward toward the front. Waist, men: level with the navel. Waist, women: at the narrowest width of the abdomen, about midway between the lower tip of the breastbone (xiphoid) and the navel, which is above the navel. Hip, women only: at the level of the greatest protrusion of the buttocks (the gluteal muscles). Stand relaxed, keep the tape level around the waist and hip, let it lie against the skin without pressing into it, and measure the waist at the end of a normal breath out. These are the sites described in the 1984 Naval Health Research Center reports; the hip site is worded in the men's report, and the everyday words (voice box, Adam's apple, breastbone, navel, buttocks, level) are this page's glosses for the reports' terms.
Can I use the Navy method to track progress over time?
This page makes no claim about that. The studies it draws on compared the equations with underwater weighing or DXA on a single occasion, and none of the parts we read measured the same people again after their body fat had changed. The 2022 Marine study states, citing the 1999 Navy document, that the estimate is reproducible to within ±1 percentage point of body fat between experienced observers; we did not find that figure in the parts of the 1999 document we read. The 1984 reports measured each site twice, took a third reading if the first two differed by more than 1 cm, and used the mean.
Why does the female formula need a hip measurement but the male formula doesn't?
The two equations were found separately, each by stepwise regression on the measurements of its own sample. The men's equation uses the abdomen at the navel, the neck and height. The women's uses the abdomen at its narrowest, the hip, the neck and height. In the men's factor analysis the hip was set aside because it correlated highly with the abdomen and the thigh; in the women's it was the thigh that was set aside, because of its high correlation with the hip. A 2022 paper on these equations adds that in women, fat distribution is more varied and less likely to favour an abdominal location.
Does this calculator work for very muscular or very lean people?
This page cannot say how the equations perform for a particular build. In the 2022 study of fit US Marines, which compared the method with DXA, lean men and women were overestimated and people with higher body fat were underestimated, and the authors conclude that the method is not suitable for applications requiring quantitative body composition assessment.
Is this the Navy SEAL body fat calculator?
No. This page uses the equations Hodgdon and Beckett published in 1984 for Navy men and women, and it contains nothing specific to SEALs. It does not describe what the Navy or any other service uses today, because we did not read their current procedures.