Body Fat Calculator (U.S. Navy Method)
Estimate your body fat percentage from a few tape-measure readings using the U.S. Navy circumference method (the Hodgdon-Beckett equations), which combine height, neck, and waist -- plus hip for women -- into a single screening figure.
How the U.S. Navy body fat method works
The Navy circumference method was developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 to estimate body fat without calipers or lab equipment. It uses log-transformed tape measurements: for men, the difference between the waist (measured at the navel) and the neck; for women, waist plus hip minus neck; combined in each case with standing height. Those figures feed a regression that predicts your body density, which is then converted to a fat percentage using the Siri equation, 495 divided by density minus 450. Measure with a snug, level tape; you can enter centimeters or inches and the tool handles the conversion.
The result is a population-level approximation, not a direct measurement. The equations were calibrated against underwater weighing in mostly young, healthy service members, and for average builds they typically land within about 3 to 4 percentage points of a DEXA scan. Because the method reads only circumferences, it can misjudge very muscular, very lean, or older bodies, and it reveals nothing about where fat sits internally. Small tape errors shift the number noticeably, so measure carefully and watch the trend across repeated readings rather than fixating on a single value.
This tool provides an informational screening estimate only. It is not a medical assessment, a diagnosis, or advice, and it cannot tell you whether your body fat level is healthy for you. If you are considering changes to your weight, diet, or training, or if you have any health condition, talk with a doctor, registered dietitian, or other qualified healthcare professional who can interpret these numbers alongside your full clinical picture.
Sources: LibreTexts (Physiology) — The U.S. Navy body-fat estimation formula
Frequently asked questions
How should I measure for the most accurate result?
Use a flexible, non-stretch tape held snug but not compressing the skin, and keep it level all the way around. Measure the neck just below the larynx (Adam's apple); the waist for men at the navel, and for women at the narrowest point; and, for women, the hip at its widest. Take each reading on bare skin after a normal exhale, repeat it two or three times, and average the results. Consistent technique matters more than any single measurement.
Is the U.S. Navy method accurate?
It is a reasonable screening estimate, not a laboratory measurement. Validation studies report agreement within roughly 3 to 4 percentage points of criterion methods such as underwater weighing or DEXA for typical adults, with larger errors at the extremes -- very muscular, very lean, or older individuals. Treat the figure as a ballpark and a way to track change over time, not an exact value.
Does this calculator use inches or centimeters?
You can enter either. The underlying Hodgdon-Beckett density equations are defined for centimeters, so if you enter inches the tool converts them first (1 inch = 2.54 cm) before applying the formula. Entering the same measurements in either unit produces the same result.
Why do men and women use different measurements?
The equations were fit separately for each sex to reflect typical differences in fat distribution. The men's formula uses waist minus neck; the women's adds the hip (waist plus hip minus neck), which improves the estimate because women tend to carry more fat around the hips. Each version has its own coefficients, so the calculator applies the one that matches your selected measurements.
