Body fat calculator

How the Navy method works

In 1984, James Hodgdon and Marcie Beckett at the Naval Health Research Center measured groups of Navy men and women with a tape and compared the results with body fat measured by underwater weighing. A few circumferences and height turned out to predict body fat well. Their equations were later refitted in inches for the Department of Defense, and those are the equations this calculator uses:

• Men: body fat % = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76
• Women: body fat % = 163.205 × log10(waist + hips − neck) − 97.684 × log10(height) − 78.387

All measurements are in inches; metric inputs are converted first. The original centimeter versions estimate body density and convert it to fat with Siri’s formula (495 ÷ density − 450). The two forms agree within about half a point for most people: for a man 180 cm tall with a 39 cm neck and a 90 cm waist, the inch equation gives 19.2% and the density equation 19.1%.

Where to measure

• Neck: just below the larynx (Adam’s apple), with the tape level.
• Men’s waist: around the abdomen at the level of the navel, stomach relaxed.
• Women’s waist: the natural waist, the narrowest point between the bottom of the breastbone and the navel.
• Women’s hips: the widest part of the buttocks, standing with feet together.
• Height: standing straight, without shoes.

Use a tape that doesn’t stretch, snug on bare skin without pressing in. Measure at the same time of day each time you check, so a change in the number reflects a change in you and not in the measuring.

Worked examples

• A man 5 ft 10 in tall with a 15-inch neck and a 34-inch waist: 86.010 × log10(19) − 70.041 × log10(70) + 36.76 = 17.5% body fat, likely between 14% and 21%. That’s in the fitness range for men (14–17%). At 180 lb, that’s about 31.5 lb of fat and 148.5 lb of lean mass.
• A woman 5 ft 5 in tall with a 13-inch neck, 30-inch waist and 38-inch hips: 28.6%, likely 25–32%, in the average range for women (25–31%). At 150 lb, that’s about 42.9 lb of fat and 107.1 lb lean.

How the waist moves the estimate

For a 5 ft 10 in man with a 15-inch neck, and a 5 ft 5 in woman with a 13-inch neck and 40-inch hips, each with everything else unchanged:

Each 2 inches on the waist adds roughly 2 to 5 points, a little less as the waist grows, because the equations work on the logarithm of the measurements. Small measuring errors move the result too, which is why the likely range matters more than the decimal.

The categories

These are the American Council on Exercise’s ranges. Essential fat is the minimum the body needs to work normally; a tape reading below it most likely means a measuring error. The chart gives ranges by sex only, not by age.

What the number can’t tell you

A tape measure can’t see where fat is or what it’s doing. The equations were built from Navy personnel, mostly young adults, so they fit some bodies better than others, and they aren’t designed for children or for pregnancy. A body fat percentage isn’t a diagnosis either: it doesn’t measure blood pressure, blood sugar or fitness. For a more precise number, ask about a lab method such as a DEXA scan.

To turn your result into calories, use the Katch-McArdle option in the TDEE calculator or compare formulas in the BMR calculator. The BMI calculator gives a different, height-and-weight view, and the protein calculator and macro calculator help plan meals. Training for something? Try the pace calculator and the heart rate zone calculator.

Sources

• Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, Report 84-11, 1984.
• Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center, Report 84-29, 1984.
• Hodgdon JA, Friedl KE. Development of the DoD body composition estimation equations. Naval Health Research Center, Technical Document 99-2B, 1999.
• Institute of Medicine. Assessing Readiness in Military Women: The Relationship of Body Composition, Nutrition, and Health, chapter 2. National Academy Press, 1998.
• Moon JR et al. Percent body fat estimations in college men using field and laboratory methods: a three-compartment model approach. Dynamic Medicine, 2008.
• Human Performance Resources by CHAMP. Measurement of body composition in the military. Uniformed Services University, 2023, updated 2026.
• Green DJ. ACE-sponsored research: can the LeanScreen app accurately assess percent body fat and waist-to-hip ratio? American Council on Exercise, 2018.

This calculator gives an estimate for adults. It isn’t medical advice. If you’re concerned about your weight or body composition, are pregnant, or have a health condition, talk to your doctor.