US Navy Body Fat Calculator
Estimate body fat from a tape measure with the US Navy formula, cross-checked against the BMI method, and see the ±5.2 point error range studies found.
That band is the ±5.2 point total error Moon et al. measured for this equation against a three-compartment reference — 8.2 kg to 16.3 kg of fat. Treat the headline number as the middle of a range, not a reading.
The BMI method uses only height, weight, age and sex — it never sees your waist, so a lifter and a sedentary person of the same weight get the same figure. The tape method reads shape but not composition. Where they diverge, the tape method is usually the better guide; where you need a number you can act on, ask for a DXA scan.
Everything is computed in your browser. No measurements are uploaded, stored or shared.
What US Navy Body Fat Calculator Does
A tape measure cannot see inside you. What the US Navy circumference method actually does is fit a curve: it takes measurements that correlate with fat distribution (neck, waist, and for women the hips) and maps them onto body fat percentages that were measured properly, by hydrostatic weighing, in the population the equation was built from. When your proportions resemble that population the estimate lands close. When they do not, it drifts, and the formula has no way of telling you which of those two situations you are in.
That is worth stating plainly because most body fat calculators report a figure to one decimal place and stop. The precision is spurious. Moon and colleagues tested the Navy and Air Force circumference equation against a three-compartment reference model and measured a total error of 5.2 percentage points, which they classified as unacceptable for the purpose. A displayed 20.4% is honestly read as "somewhere around 15% to 26%".
None of which makes the measurement useless. A consistent method applied to the same body over months tracks change well even when its absolute accuracy is poor, because the error is largely systematic: it sits in roughly the same place each time. The number to watch is the direction of travel rather than the decimal.
How to Use US Navy Body Fat Calculator
- Choose metric or imperial, then your biological sex, since the formula uses different constants for each
- Measure your neck below the larynx and your waist at the navel, keeping the tape level and snug but not tight
- Enter height, weight, age and those measurements (women also add hip circumference at the widest point)
- Read the percentage together with the range beneath it, and compare it against the BMI-method figure
Formula Used by US Navy Body Fat Calculator
US Navy circumference method — men (centimeters)
BF% = 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
- waist
- Circumference at the navel, in centimeters
- neck
- Circumference just below the larynx, in centimeters
- height
- Standing height, in centimeters
- log₁₀
- Base-10 logarithm
Worked example
Height 178 cm, neck 39 cm, waist 92 cm
- waist − neck = 92 − 39 = 53 cm
- log₁₀(53) = 1.72428, so 0.19077 × 1.72428 = 0.32895
- log₁₀(178) = 2.25042, so 0.15456 × 2.25042 = 0.34783
- denominator = 1.0324 − 0.32895 + 0.34783 = 1.05128
- 495 / 1.05128 = 470.86, minus 450
Result: 20.9% body fat, read as roughly 15.7% to 26.1% once the method error is applied
US Navy circumference method — women (centimeters)
BF% = 495 / (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
- hip
- Circumference at the widest point of the hips, in centimeters
- waist + hip − neck
- The combined term the female equation is fitted against
Deurenberg BMI method — the cross-check on this page
BF% = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex: 1 male, 0 female)
- BMI
- Weight in kilograms divided by height in meters squared
- age
- Age in years
Worked example
The same man: 178 cm, 82 kg, age 35
- BMI = 82 / 1.78² = 25.9
- 1.20 × 25.9 = 31.08
- 0.23 × 35 = 8.05
- 31.08 + 8.05 − 10.8 − 5.4
Result: 22.9%, about 2 points above the tape estimate, and unchanged no matter what his waist measures
How far each method sits from a laboratory reference
Total error against a Siri three-compartment model in 31 college-age men. The authors treated anything above roughly 3.5 points as unacceptable for individual assessment.
| Method | Total error (percentage points) | Verdict in the study |
|---|---|---|
| Bioelectrical impedance (BIA-AK / BIA-Lohman) | 2.1 | Acceptable |
| Hydrostatic weighing | 2.5 | Acceptable |
| Air-displacement plethysmography (Bod Pod) | 2.7 | Acceptable |
| Army circumference equation | 4.7 | Unacceptable |
| Marine Corps circumference equation | 4.7 | Unacceptable |
| Near-infrared interactance | 5.1 | Unacceptable |
| Navy / Air Force circumference equation | 5.2 | Unacceptable |
The two methods on this page, as the waist changes
Same man throughout: 178 cm, 82 kg, neck 39 cm, age 35, BMI 25.9. Only the waist moves.
| Waist | Navy tape method | Deurenberg BMI method | Difference |
|---|---|---|---|
| 76 cm | 7.9% | 22.9% | −15.0 points |
| 84 cm | 14.9% | 22.9% | −8.0 points |
| 92 cm | 20.9% | 22.9% | −2.1 points |
| 100 cm | 26.1% | 22.9% | +3.2 points |
| 108 cm | 30.8% | 22.9% | +7.9 points |
What one centimeter of tape error costs you
Starting from 178 cm height, 92 cm waist, 39 cm neck, which gives an estimate of 20.9%.
| Measurement error | Result | Shift |
|---|---|---|
| Waist 2 cm too small | 19.4% | −1.42 points |
| Waist 1 cm too small | 20.1% | −0.71 points |
| Measured correctly | 20.9% | — |
| Waist 1 cm too large | 21.5% | +0.69 points |
| Neck 1 cm too small | 21.5% | +0.69 points |
| Neck 2 cm too small | 22.2% | +1.38 points |
How to Read Your Result
Read the band, not the decimal
At an estimated 20% body fat, the 5.2-point method error spans a real range of fat mass that widens with body size: about 6.2 kg for a 60 kg person, 7.8 kg at 75 kg, 9.4 kg at 90 kg and 10.9 kg at 105 kg. Two people shown the same percentage can be carrying very different amounts of fat, and the calculator cannot distinguish them. This is why the figure is useful for tracking and poor for classifying.
Careful measuring helps less than you would hope
A centimeter of error on the waist moves the answer by roughly 0.7 of a percentage point, and the same error on the neck moves it by a similar amount in the opposite direction, so sloppy tape work can easily shift a result a point or two. Worth avoiding, but note the scale: even flawless measurement leaves the roughly five-point method error entirely intact. Precision in the input does not buy accuracy in the output.
The unit trap
These constants are calibrated for centimeters. Feeding inches into them without converting is a genuinely easy mistake and it fails quietly: the same man at 70 in, 36.2 in and 15.4 in returns 14.3% instead of the correct 20.9%, a plausible-looking answer that is six and a half points wrong. This calculator converts imperial input to centimeters before applying the formula. If you are checking the arithmetic yourself in a spreadsheet, convert first.
Where the categories come from, and what they are worth
The fitness-industry bands shown with your result are conventions rather than clinical thresholds. Gallagher and colleagues took a more careful approach, deriving provisional healthy ranges by linking body fat to the established BMI cutoffs across 1,626 adults measured by four-compartment models and DXA, and found that the healthy range genuinely shifts with sex, age and ethnicity. A single fixed chart applied to everybody is a simplification, and the further you sit from a young, white, average-build reference population, the more of a simplification it becomes.
Why the military standard is contested
Circumference equations carry real consequences for service members, and their accuracy has been challenged from inside the services. A Naval Submarine Medical Research Laboratory validation study of personnel flagged as over the standard found the circumference equation produced a false-positive rate between 6.8% and 18%, and its authors advised caution in using the method for individual career decisions. If a tape-measure result matters to your job, ask for a laboratory measurement rather than accepting the estimate.
Limitations & Accuracy Notes
- The equation was developed on US Navy personnel and fits people who resemble that population best. Very muscular builds are typically overestimated, since a thick neck lowers the result while a broad, muscular waist raises it; older and less active people with the same measurements are often underestimated.
- The Moon comparison that supplies the error figures used 31 Caucasian college-age men. It is the clearest available like-for-like test of the military equations, but a small single-population study is not the last word, particularly for women.
- The Deurenberg cross-check inherits every weakness of BMI. It cannot distinguish muscle from fat, so it returns the same answer for two people of identical height, weight, age and sex however differently they are built.
- Nothing here diagnoses anything. Body fat percentage is one crude marker among many, and it says nothing about where fat is stored: visceral fat around the organs carries different risk from subcutaneous fat, and no tape measure separates them.
- For a number you can genuinely act on (an athlete making weight, a clinical assessment), use DXA or hydrostatic weighing. Both are widely available and both were measured at roughly half the error of any tape method.
Frequently Asked Questions
How accurate is the US Navy body fat calculator?
Less accurate than most sites claim. Moon and colleagues (Dynamic Medicine, 2008) compared the Navy/Air Force circumference equation against a Siri three-compartment model in 31 college-age men and measured a 5.2 percentage-point total error, which they classed as unacceptable. Hydrostatic weighing came in at 2.5 points. Treat a tape-measure figure as the middle of a range roughly five points wide rather than as a reading.
What is a healthy body fat percentage?
There is no single agreed set of ranges. Gallagher and colleagues (American Journal of Clinical Nutrition, 2000) built provisional ranges by linking body fat to established BMI cutoffs, and found the healthy range shifts with sex, age and ethnicity, so a figure that is unremarkable for a 60-year-old may not be for a 25-year-old. The bands this tool shows are the widely used fitness-industry categories, useful for tracking your own trend rather than for diagnosis.
Why do the two methods on this page disagree?
They measure different things. The Navy formula reads your shape from neck, waist and (for women) hip circumference. The Deurenberg BMI equation uses only height, weight, age and sex, so it cannot see where the weight sits: a heavily muscled person and a sedentary person of the same height and weight get an identical answer from it. A large gap between the two usually means your build is unusual for your weight.
Does measuring more carefully make the result accurate?
It helps, but not enough to close the gap. One centimeter of tape error on the waist moves the result about 0.7 of a percentage point, and the same error on the neck moves it a similar amount in the opposite direction. Even perfect tape work leaves the roughly five-point method error untouched. For a number precise enough to act on, you need a DXA scan or hydrostatic weighing.
How accurate is the tape-measure method?
The US Navy circumference method is typically within about three to four percentage points of a DEXA scan: good enough to track a direction over months, but not good enough to treat a single reading as exact. Consistency in how you measure matters more than the absolute figure.
Where exactly should I measure?
The method specifies sites precisely: neck below the larynx, waist at the navel for men and at the narrowest point for women, hips at the widest. Measuring a centimeter off, or pulling the tape tight, changes the result more than a month of training will.
Why do men and women have different healthy ranges?
Because essential fat (the minimum required for normal physiological function) is substantially higher in women, largely for reproductive reasons. A percentage that is lean-but-healthy for a man can be below the essential minimum for a woman, which is why the bands are not interchangeable.
Why is this better than BMI?
Because it attempts to separate fat from everything else. BMI cannot distinguish muscle from fat and misclassifies muscular people as overweight. Body fat percentage is more informative about an individual, even measured imperfectly.
Why does my reading jump around day to day?
Mostly measurement error and hydration. Day-to-day changes in actual body fat are far too small to detect with a tape measure, so only a trend over several weeks means anything.
Is my data stored?
No. Measurements are used in your browser and never transmitted.
References & Further Reading
- Moon JR et al. — Percent body fat estimations in college men using field and laboratory methods — Dynamic Medicine 2008;7:7, the source of the total-error figures for every method in the comparison table
- Shake CL et al. — Predicting percent body fat from circumference measurements — Military Medicine 1993;158(1):26-31, the source of the 6.8–18% false-positive finding on the Navy equation
- Gallagher D et al. — Healthy percentage body fat ranges — Am J Clin Nutr 2000;72(3):694-701, with provisional healthy ranges by sex, age and ethnicity, n=1,626
- Deurenberg P et al. — Body mass index as a measure of body fatness — Br J Nutr 1991;65(2):105-114, the BMI-based equation used as the cross-check on this page