US Navy Body Fat Calculator
Estimate your body fat percentage, fat tissue weight, and lean mass using the standard anthropometric tape method developed by the Naval Health Research Center
Anthropometric Measurements
Medical Note: The original equations were validated against underwater weighing with a standard error of roughly 3–4 percentage points; individual error can be larger. Consult a medical professional before starting aggressive dietary or exercise changes.
How to use this tool
- Choose Metric or US units and select Male or Female.
- Enter height and weight, then measure the neck just below the larynx and the waist (men at the navel, women at the narrowest point), with the tape horizontal and not pulled tight.
- Women also enter the hip circumference at its widest point.
- Read the body fat percentage, the fat and lean mass, and the range it falls in.
Worked example
A man of 178 cm and 80 kg with a 39 cm neck and 86 cm waist has a waist-minus-neck difference of 47 cm. The Hodgdon–Beckett equation gives about 16.4% body fat, which the tool places in its Fitness range (14%–17%): 13.1 kg of fat and 66.9 kg of lean mass. A 1 cm measurement error can move the result by a noticeable fraction of a percentage point, so measure the same way each time, ideally in the morning. It is an estimate based on population averages, not a medical measurement, and it is less reliable for very muscular or very lean people.
Why this tool exists and where its numbers come from
A tape measure is the cheapest way to estimate body fat. The men's equation comes from a 1984 Naval Health Research Center report (602 male personnel); it is a field estimate with a margin of error, not a clinical measurement, and this site is not affiliated with the U.S. Navy.
Sources
For the full method, see the Methodology section just below.
Methodology
The Hodgdon–Beckett body fat equations were developed by researchers at the Naval Health Research Center in 1984 as a low-cost field estimate that does not need underwater weighing. This site is not affiliated with the U.S. Navy, and the armed forces have since updated their own body composition methods.
Tape-measure habits that move the Navy estimate
The equation uses only height and circumferences, so small measuring habits matter more than the arithmetic. These examples come straight from the tool's own formulas.
- Measuring a woman's waist at the navel. Women use the narrowest point of the torso. With height 165 cm, neck 33 cm and hips 98 cm, a 75 cm waist gives 28.4%; measuring 85 cm at the navel gives 33.3%, which jumps from the Average range to the top one.
- Typing inches while Metric is selected. A man of 70 in with a 15 in neck and 34 in waist gets 17.4% in US units, but the same numbers read as centimeters give 11.1%. Nothing looks broken, so check the unit toggle first.
- Pulling in or pushing out the stomach. For a 178 cm man with a 38 cm neck, a 90 cm waist gives 20.1%. A 88 cm waist gives 18.7% and a 92 cm waist gives 21.5%, a spread of 2.8 points from a few centimeters.
- Forgetting the hips after choosing Female. The women's equation needs the hip value, so an empty field shows dashes, as does a man's waist that is not larger than the neck.
- Reading the wrong band. The ranges differ by sex: Fitness is 14%–17% for men and 21%–24% for women.
This is an estimate for information only, not medical advice or a diagnosis.
Recommended Measuring Tools
Tape measures, a skinfold caliper and a bioimpedance scale. Measuring the same way each time matters more than the tool.
iBayam Ergonomic Retractable Body Tape Measure (2-Pack)
Two retractable body tape measures with a pin lock and push button, according to the listing, for measuring neck, waist and hips the same way each time.
MEDca Body Fat Caliper & Tape Measure Set
A skinfold caliper and tape measure set with charts, according to the listing. Skinfold readings depend a lot on technique.
GE Smart Digital Bioimpedance Body Composition Scale
A bioimpedance scale with a large display and several body-composition readings, according to the listing. Its body-fat figure is an estimate by a different method from the Navy formula.
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Frequently asked questions
How accurate is the US Navy Body Fat formula compared to DEXA scans? ▼
The original equations were validated against underwater (hydrostatic) weighing with a standard error of roughly 3 to 4 percentage points, and comparisons with DEXA scans can show similar or larger differences for some people. Keeping the tape at a consistent tension matters.
Where exactly should measurements be taken on the body? ▼
Neck: horizontally just below the thyroid cartilage (Adam's apple), with head upright. Waist (Men): horizontally across the navel at the end of normal expiration. Waist (Women): at the narrowest anatomical point above the navel. Hips (Women): at the widest circumference over the gluteal muscles.
Can this calculator diagnose obesity or health conditions? ▼
No. This tool provides an informational biometric estimate. While body fat percentage is a helpful health indicator, it does not evaluate metabolic markers, blood pressure, or cardiovascular risk. Always seek professional advice from a doctor for medical diagnoses or before starting aggressive weight-loss protocols.
Can you show a worked example, and how much does a measuring error matter? ▼
A man 178 cm tall with a 90 cm waist and a 38 cm neck gets %BF = 495 / (1.0324 − 0.19077 × log10(52) + 0.15456 × log10(178)) − 450, which is about 20.1%. Measuring the waist 1 cm larger moves the result to about 20.9%, and a neck 1 cm larger lowers it to about 19.4%. A woman of 165 cm with a 75 cm waist, 98 cm hips and a 33 cm neck gets about 28.4%. Errors of 1 to 2 cm are easy to make with a tape, so read the result as a range of a few points, not an exact number.
Why does the tool sometimes show dashes instead of a result? ▼
The result is hidden when a field is empty or zero, when the waist is not larger than the neck for men, or when the equation returns a value below 2% or above 60%, which signals a likely measuring or entry mistake. The category bands (such as Fitness or Average) are general fitness ranges and not a medical diagnosis. They differ for men and women because women naturally carry more essential fat. Pregnancy, growth in teenagers and some medical conditions are not covered by the equation.