Army Body Fat Calculator

By Jack Kyle — Jack Kyle writes about strength training and lifting math — calculators, programming and standards — with a focus on honest numbers and practical guidance.

Intro

Tape-measure body fat estimates have one real advantage: you can do them in two minutes with a tape and no special equipment. They also have one real weakness: a small measuring slip moves the result more than most people expect. This calculator gives one estimate from one set of measurements. You enter height, weight, and a few circumference measurements, and it returns the Army circumference method result — the Army tape sites applied to the Hodgdon–Beckett equation — plus an honest range of about ±3 percentage points that reflects tape-measurement error. The Navy protocol uses the same equation and differs only in the tape site (waist at the narrowest point, not the navel), so a second number from the same waist input would be false precision. Use the estimate to track change over time, to feed an FFMI calculation, or to set a starting point for a training block. Use the estimate to track change over time, to feed an FFMI calculation, or to set a starting point for a training block. Do not treat any single tape reading as exact, and do not use it to judge anyone’s health or fitness on its own.

Calculator

Strength tools / Body fat

Army Body Fat Calculator

Army circumference estimate (one number) with an honest range. Estimate only.

Measure with a tape: neck below the Adam's apple, waist at the navel, hip at the widest point (women). Keep the tape snug, not tight. Enter the NAVEL waist measurement — the Army tape site.

Estimates only — see our Disclaimer.

How it works

The method

  • Army circumference method (AR 600-9). The Army’s published circumference method uses height, weight, and tape measurements — neck and waist for men, neck, waist, and hip for women — to estimate body fat percentage. The tool applies the Army’s published calculation.
  • The equation. The Hodgdon–Beckett circumference equation. For men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. All measurements in centimetres. The Navy protocol uses the same equation and differs only in the tape site (waist at the narrowest point, not the navel) — which is why this tool shows one Army-site estimate rather than two near-identical numbers from one waist input.

One estimate is shown, with an honest range of about ±3 percentage points for tape-measurement error. It gives no pass/fail verdict and no health diagnosis. This is a planning estimate, not medical advice.

Measurement sites

  • Neck. Around the neck, just below the Adam’s apple, tape flat and level, head straight.
  • Waist. At the navel. This is the waist site for this calculator. Measure at the navel, not at the narrowest point and not at the belt line. Keep the tape level, breathe normally, and do not pull the tape tight or hold your breath.
  • Hip (women). Around the widest part of the hips and buttocks, tape level.
  • Height and weight. Height in centimetres, weight in the unit you train in. Both feed the estimate, so enter current numbers.

How to use the result

Work with the range, not just the point estimate. If the tool shows 18% with a range of 15–21%, treat 18% as the planning number and the range as the honest uncertainty from tape error. Watch how the range moves over weeks. A single reading is a starting point. A series of readings taken the same way, by the same person, at the same time of day, shows change far better than any one reading.

Honest limits

  • Tape methods estimate body fat from circumferences. They do not measure body fat directly, and they cannot match a lab method.
  • A 1 cm slip at the waist moves the result by a visible amount. Measure twice, and use the same sites each time.
  • The equations were fitted to group data. They are less reliable at very low or very high body fat, and for bodies far from the groups the equations were built on.
  • This calculator gives no health verdict and no medical advice. For health questions, speak to a qualified professional.

FAQs

Why does this page show one estimate, not Army and Navy side by side?

Because both protocols use the same Hodgdon–Beckett equation and differ only in the tape site — Army measures the waist at the navel, Navy at the narrowest point. From a single waist input, a second number would be near-identical arithmetic, not a second opinion. This tool gives one Army-site estimate plus an honest range of about ±3 percentage points for tape-measurement error, which is the real uncertainty.

Where exactly do I measure my waist?

At the navel. Stand relaxed, tape level around the body at the navel, breathe normally, and read the tape without pulling it tight. Measuring at the narrowest point or at the belt line gives a different number and breaks the comparison.

Should I measure in the morning or after training?

Pick one time and keep it. Morning, before food, is the most repeatable for most people. After training, a meal, or a large drink shifts waist and weight readings enough to blur small changes.

How often should I re-measure?

Every two to four weeks is enough for tracking change. Weekly readings add measuring noise. Daily readings add more noise still.

Can I use this estimate in the FFMI calculator?

Yes. Body fat percentage is the input the FFMI calculation needs alongside height and weight. Take the tape estimate from this page and enter it there. The FFMI page shows the range that follows from normal body-fat input error.

Is this a pass/fail test?

No. This page gives an estimate for planning and tracking. It does not grade, pass, or fail anyone, and it does not diagnose anything.