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Body Fat Calculator: US Navy Circumference Method

Enter your waist, neck and height (plus hip for women) to estimate body fat percentage with the US Navy circumference equations. You get the percentage, where it sits against published categories, and the arithmetic to work out lean mass from your weight.

  • Calculator
  • About 3 min
  • Hodgdon and Beckett 1984 Navy equations
  • Runs in your browser, nothing is sent
  • Medical review: Medical review pending
Open the calculator

What this calculator works out

Scales measure weight, not composition. Two people of the same height and weight can carry very different amounts of fat. The Navy equations use the fact that fat accumulates predictably at the waist and hip relative to frame size, so a few tape measurements predict percent body fat within a few points of underwater weighing for most adults.

  1. 1

    Body fat percentage

    The share of your body weight that is fat, estimated from circumferences and height with the sex-specific Navy equation. The published standard error is about 3.5 percentage points, which is similar to skinfold calipers and most consumer bioimpedance scales.

  2. 2

    Category band

    Where the estimate sits against the American Council on Exercise categories (essential fat, athletes, fitness, average, above the healthy range), which differ for men and women because women carry more essential fat. The band text gives both readings.

  3. 3

    Lean mass arithmetic

    Lean mass is weight minus fat mass: weight times (1 minus body fat as a fraction). The formula here returns the percentage; the section below shows the two-line calculation, and the lean body mass calculator on this site does it from weight and body fat directly.

How this compares with a typical online quiz

FeatureTypical free quizRegenerated.com
Equation named and shownRarelyHodgdon and Beckett 1984, with the worked example
Error bar statedNoYes, about 3.5 points standard error
Measurement protocol explainedSometimesYes, site by site, from the Navy procedure
Category source citedRarelyACE categories and Gallagher 2000 ranges
Inches and centimeters handledSometimesYes, conversion in every field
Answers sent to a serverOftenNever; scored in your browser, counts-only events

How to take the measurements

The equations were derived from a specific measurement procedure, and small changes in tape position shift the result by one or two points. Use a flexible, non-stretch tape, keep it level with the floor, snug against the skin without compressing it, and read at the end of a normal breath out. Neck: just below the larynx (the Adam's apple), with the tape sloping very slightly downward to the front. Waist for men: horizontally at the level of the navel, standing relaxed, not pulled in. Waist for women: at the narrowest point of the natural waist, usually a little above the navel. Hip for women: around the largest circumference of the buttocks, feet together. Height: without shoes, heels together, standing straight.

Measure each site twice and average; if the two readings differ by more than about 1 cm (half an inch), measure a third time. Measure at the same time of day for repeat readings, since the waist changes with meals and fluid. The equation is sensitive to the difference between waist and neck for men, and to waist plus hip minus neck for women, so an error of 2 cm at the waist moves the result by roughly one percentage point.

From percentage to fat mass and lean mass

Fat mass equals body weight times body fat percentage divided by 100. Lean mass, sometimes called fat-free mass, is everything else: muscle, bone, organs, water and connective tissue. For example, an 80 kg (176 lb) man at 16.1 percent carries 80 x 0.161 = 12.9 kg (28 lb) of fat and 80 - 12.9 = 67.1 kg (148 lb) of lean mass. A 62 kg (137 lb) woman at 28.4 percent carries 17.6 kg (39 lb) of fat and 44.4 kg (98 lb) of lean mass.

Lean mass is the number that matters for protein targets, for resting energy expenditure (the Katch-McArdle equation uses it directly) and for judging whether weight loss on a GLP-1 medicine or any diet is coming from fat or from muscle. Repeating this calculation every four to six weeks during a weight change is a reasonable home check; a falling weight with a steady or rising lean mass figure is the pattern to aim for, and a lean mass that falls as fast as weight is worth raising with the clinic.

What the categories mean and where they come from

The band on the result page uses the categories published by the American Council on Exercise. Women: essential fat 10 to 13 percent, athletes 14 to 20, fitness 21 to 24, average 25 to 31, and 32 or more above the healthy range. Men: essential fat 2 to 5, athletes 6 to 13, fitness 14 to 17, average 18 to 24, and 25 or more above the healthy range. These are fitness-industry conventions rather than medical cut-offs, and they were not derived from the Navy equations, so they orient rather than define.

The most-cited research ranges come from Gallagher and colleagues (2000), who linked body fat to BMI categories across adults in the United States, the United Kingdom and Japan. For adults aged 20 to 39 they placed the healthy range at about 8 to 20 percent for men and 21 to 33 percent for women, rising by a few points in each older decade. The two schemes overlap heavily in the middle; the Gallagher ranges are more generous at the upper end for women. A result near a boundary is not a different category on a different day; it is within the equation's error bar.

Methodology and sources

The calculator implements the circumference equations developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 (reports 84-11 for men and 84-29 for women), which the US Navy adopted for body composition assessment. They were derived by regression against underwater weighing in Navy personnel, with a correlation of about 0.90 and a standard error of about 3.5 percentage points for men and about 3.7 for women. The equations assume adults of roughly military age and build; they are less accurate in very lean athletes, in people with a great deal of abdominal fat relative to the rest of the body, in older adults, and in anyone whose fat distribution is unusual for their sex. They were not derived in pregnancy and should not be used there.

Men: percent fat = 495 / (1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)) - 450. Women: percent fat = 495 / (1.29579 - 0.35004 x log10(waist + hip - neck) + 0.22100 x log10(height)) - 450, all in centimeters. Worked example: a man with an 85 cm waist, 38 cm neck and 180 cm height gives 495 / (1.0324 - 0.19077 x log10(47) + 0.15456 x log10(180)) - 450 = 16.1 percent. A woman with a 75 cm waist, 97 cm hip, 32 cm neck and 165 cm height gives 495 / (1.29579 - 0.35004 x log10(140) + 0.22100 x log10(165)) - 450 = 28.4 percent. Inches are converted at 2.54 cm per inch before the equation runs.

The category bands are the American Council on Exercise general body-fat categories, with the Gallagher 2000 healthy ranges quoted in the section above for comparison. Neither set was validated against the Navy equations specifically, and both are conventions for orientation rather than clinical thresholds. The equation returns a point estimate; a true value anywhere within about 3.5 points of it is consistent with the measurement, which is why a change of one or two points between readings does not mean anything on its own.

Medical review: Medical review pending. Last updated .

References

  1. Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Report No. 84-11. San Diego, CA: Naval Health Research Center; 1984.
  2. Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy women from body circumferences and height. Report No. 84-29. San Diego, CA: Naval Health Research Center; 1984.
  3. Gallagher D, Heymsfield SB, Heo M, Jebb SA, Murgatroyd PR, Sakamoto Y. Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. Am J Clin Nutr. 2000;72(3):694-701. https://doi.org/10.1093/ajcn/72.3.694
  4. Jackson AS, Pollock ML. Generalized equations for predicting body density of men. Br J Nutr. 1978;40(3):497-504. https://doi.org/10.1079/BJN19780152
  5. Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Med Sci Sports Exerc. 1980;12(3):175-181.

Body Fat Calculator: US Navy Circumference Method FAQ

In the original Navy samples the equations predicted underwater-weighing body fat with a standard error of about 3.5 percentage points, meaning roughly two thirds of people fall within 3.5 points of the estimate and nearly all within 7. That is comparable to skinfold calipers in trained hands and better than most bathroom bioimpedance scales. It is less accurate at the extremes: very lean, very muscular, or carrying most fat at the abdomen.

A caliper method that measures skinfold thickness at three sites (chest, abdomen and thigh for men; triceps, suprailiac and thigh for women), sums them, converts to body density with the Jackson and Pollock equations (1978 for men, 1980 for women) and then to percent fat with the Siri equation. It is about as accurate as the Navy method when the calipers are used by someone trained, and worse when they are not. It is not in this calculator because it needs calipers and practice; the tape method needs neither.

Women store proportionally more fat at the hips and thighs, so the hip circumference carries information about total fat that the waist alone misses. The men's equation was derived without it. The calculator asks everyone for a hip value so the form is the same for both, but it only uses it when the sex field is set to female.

The equation runs in centimeters. Multiply inches by 2.54: a 34 inch waist is 86.4 cm, a 15 inch neck is 38.1 cm, and 5 feet 11 inches (71 inches) is 180.3 cm. Each input's help line repeats the conversion.

Conventions differ. The ACE categories put the fitness and average ranges at 14 to 24 percent for men and 21 to 31 percent for women. Gallagher and colleagues (2000) put the healthy range for adults aged 20 to 39 at about 8 to 20 percent for men and 21 to 33 percent for women, widening with age. Health risk tracks abdominal fat more closely than total fat, which is why the waist-to-height ratio is worth checking alongside this number.

Yes. Your answers and the numbers you enter are scored in your browser and are never sent to us. They stay in this browser tab so you can return to your result, and closing the tab clears them. The only thing the page sends us is a counts-only event: which test was started or completed, the result band and the headline number, with no answers, no entered values and no account. There is nothing to sign up for.

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Important: This calculator is educational arithmetic on measurements you enter. It is an estimate of body fat percentage, not a measurement of it, not an assessment of your health and not a recommendation for any diet, medicine or treatment. The category bands are published conventions for orientation. Only a clinician who knows your history can interpret body composition alongside your other results. If your symptoms are severe or sudden, seek urgent medical care.