Body-Fat Measurement Methods: DEXA, Calipers, BIA

Every way to measure body fat, ranked by accuracy, plus which methods the military accepts for the secondary body-fat evaluation.

By The VivMetric Editorial Team · independent editorial research project

DEXA (dual-energy X-ray absorptiometry)

The reference standard: a full-body X-ray scan that reports fat, lean, and bone with high precision. Accepted as a supplemental assessment under AR 600-9 where available at the installation.

Air-displacement plethysmography (Bod Pod)

Uses air displacement to measure body density. Close to DEXA in accuracy for most people and also accepted as a supplemental method under AR 600-9.

Bioelectrical impedance (BIA / InBody)

Passes a weak current through the body; the InBody 770 is explicitly named in AR 600-9 as an accepted supplemental device. Home scales using BIA are less accurate and hydration-dependent.

Skinfold calipers

Measures fat under the skin at 3–7 sites. Accurate when done by a skilled technician (±3%), less so for self-measurement. Used in NFPA fitness testing contexts.

The Navy circumference formula

The tape-only method most services use for the secondary evaluation: height, neck, waist (and hip for women) feed a validated regression. Quick and repeatable, within ±3% of DEXA for most people when measured carefully.

Estimate body fat (Navy method)

Estimate body-fat % with the exact U.S. Navy circumference formula (neck + waist; hips for women).

Sex

Height (in)

Neck (in)

Waist at navel (in)

Result

Estimated body-fat %17.5%

±3–4% versus DXA. Women must include hip. This is the Navy method used as a cross-branch estimate; your service runs its own official assessment.

About this calculator

Estimates body-fat percentage with the U.S. Navy circumference method, using neck (and waist; hips for women) measurements.

The formula

Navy method: men BF% ≈ 86.010·log10(waist−neck) − 70.041·log10(height) + 36.76; women add a hip term. Keep units consistent (inches or cm).

Frequently asked questions

Q: How accurate is it?

A: Typically ±3–4 percentage points versus a DXA scan. Treat it as an estimate, not a lab measurement.

Q: Why include hip for women?

A: The Navy formula uses hip circumference for female measurements to account for fat distribution.

Q: What is a healthy range?

A: Roughly 10–20% for men and 18–28% for women is considered fit; your service uses its own official tables.

How to read the result

A circumference estimate is a model rather than a measurement. The Navy equation was derived by fitting tape readings against a reference method across a large sample, so it reproduces the average relationship rather than the composition of any single person. Expect roughly three to four percentage points of error against a laboratory standard, and expect that error to grow for anyone whose fat distribution sits far from the average the equation was built on.

Technique moves the result more than most people expect. The neck tape goes below the larynx and slopes downward at the front, the waist tape sits at the navel, and for women the hip tape is taken at the widest point. A single inch of error on the neck measurement shifts the estimate by about a percentage point, which is how the same person can be measured twice and receive two different answers. Track change over time with one method and treat a comparison between two different methods as meaningless.

Quick answers

Which method will my branch actually use?

Typically the tape-based Navy formula. If you dispute the result, AR 600-9 allows a supplemental DXA, Bod Pod, or InBody 770 assessment where reasonably available.

How accurate are the results?

DEXA is the gold standard (±1–2%); calipers and BIA ±3% with good technique; home BIA scales are the least reliable and can swing several points with hydration.

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