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The US Navy tape-measure method for estimating body fat

You cannot weigh fat directly at home. What you can do is measure a few body circumferences with a tape and put them into a formula built from people whose body fat was measured properly. The US Navy method is the best-known of these formulas.

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Where it comes from

In 1984 James Hodgdon and Marcie Beckett at the US Naval Health Research Center measured Navy personnel two ways: with a tape, and by underwater weighing, which was the standard laboratory method for body fat at the time. They then found the combination of circumferences that best predicted the laboratory result. For men that was the neck and abdomen. For women it was the neck, waist and hips. Height is used in both.

The original reports give the equations in centimetres, as a body-density figure that is then converted to a body-fat percentage. The version almost everyone uses today does the same thing in one step, in inches:

Men: body fat % = 86.010 × log₁₀(waist − 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. To use centimetres, divide each one by 2.54 first.

Where the tape goes

The Navy's own procedure puts the tape here:

  • Neck: just below the larynx (the Adam's apple), with the tape at right angles to the neck rather than level with the floor.
  • Abdomen, for men: across the belly button.
  • Waist, for women: the narrowest point, usually about halfway between the belly button and the bottom of the breastbone.
  • Hips, for women: the widest point of the buttocks, seen from the side.

The Navy takes each measurement twice. If the two differ by more than an inch it takes a third and uses the average. It is a good habit to copy: stand relaxed, keep the tape snug but not pressing in, and don't pull your stomach in.

A worked example

A man who is 180 cm tall with a 38 cm neck and an 86 cm abdomen: in inches that is 70.9, 15.0 and 33.9. Put into the men's formula, those give an estimate ofabout 16.9% body fat.

Now measure his abdomen at 88 cm instead of 86 — the kind of difference a slightly lower tape or a big lunch makes — and the estimate becomes 18.5%. Two centimetres of tape moved the answer by one and a half percentage points. That sensitivity is the most useful thing to understand about this method.

How accurate is it?

Against underwater weighing, the original men's equation had a standard error of estimate of about 3.5 percentage points. In plain terms, about two people in three get a tape estimate within 3.5 points of their laboratory figure, and the rest are further out than that.

A 2023 study of 1,407 US Army recruits compared the same equations with DXA scans, the modern reference method. The standard error was 3.4 points for men and 4.1 for women. The study also followed the recruits through eight weeks of basic training, and found that the tapeunderestimated the change in body fat in men and did not detect the change in women at all, even though the scans showed a clear drop in both (DXA: about 3 to 4 points; tape: 2.2 points in men, none in women). So the method is a reasonable one-off estimate, but it is slow to show short-term change.

It also cannot tell fat from muscle. A lifter with a thick neck will read lower, and anyone who carries more fat on the arms and legs than round the middle may read lower than they really are, because those areas are never measured.

The military has since moved on

The formula has been retired by the people it was written for. In 2023 the US Army replaced it with a simpler equation that uses body weight and an abdominal measurement. From January 2026 the US military moved to waist-to-height ratio as its first screen, and the Army now uses that as its only screening measurement. The Navy formula is still widely used outside the forces, because it needs nothing but a tape measure.

Getting the most out of it

  • Measure the same way every time: the same tape, the same landmarks and the same time of day, ideally in the morning before eating.
  • Trust the trend more than the number. Given the error above, a single reading of 18% could really be 15% or 21%. Readings taken the same way over months are far more informative, as long as you allow for the method being slow to show short-term change.
  • Don't compare methods. A tape estimate, a smart-scale reading and a caliper reading of the same person on the same morning will usually disagree. Pick one method and stick with it.

Sources

  • Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Report 84-11, Naval Health Research Center, San Diego, 1984 (and the companion report for women, 84-29).
  • Foulis SA, Friedl KE, Spiering BA, et al. “Body composition changes during 8 weeks of military training are not accurately captured by circumference-based assessments.” Frontiers in Physiology, 2023;14:1183836.
  • US Navy. Physical Readiness Program Guide 4: Body Composition Assessment (measurement landmarks and repeat-measurement rule).
  • US Army. ALARACT 046/2023, Army Directive 2023-11 (the 2023 equation); US Under Secretary of Defense memorandum of 18 December 2025 and Army Directive 2026-13 (the move to waist-to-height ratio).

This page is reference information about how a measurement is taken and what the research says about it. It is not medical advice, and no figure on it is a diagnosis. Talk to a doctor, nurse or registered dietitian about your own health.