Estimate your body fat percentage from three tape measurements with the U.S. Navy method — plus your fat mass, lean mass, and where you sit on the ACE ranges.
Your measurements
cm
cm
cm
kg
years
Body fat — U.S. Navy method
16.4%
Fitness range (ACE)
Fat mass
12.8kg
Lean mass
65.2kg
muscle, bone, organs, water
BMI-method estimate
20.2%
Deurenberg, for comparison
Where you sit — ACE categories (men)American Council on Exercise ranges. Essential fat is the physiological minimum — lower is not better below that line.
What your weight is made of
16.4%body fat
Fat mass12.8 kg
Lean mass65.2 kg
Lean mass is everything that is not fat — muscle, bone, organs and water. Hover a segment for its share.
What your waist does to the number
With your height and neck fixed, the Navy estimate is driven almost entirely by the waist. Hover the curve to see the body fat reading at any waist size — useful for setting a tape-measure target instead of a scale target.
Tape estimates carry roughly ±3–4% error against a DEXA scan, and they are most reliable for tracking change: measure the same spots, same time of day, and watch the trend rather than any single reading.
How a tape measure estimates body fat
The U.S. Navy needed a body fat method that thousands of sailors could be assessed with quickly, cheaply and repeatably — no calipers, no tanks, no scans. Hodgdon and Beckett solved it in 1984 by regressing simple circumference measurements against underwater weighing, the gold standard of the day. The insight is that fat and lean tissue change different circumferences: gaining fat shows up at the waist and hips, while the neck tracks lean frame size. The gap between them, adjusted for height, predicts body density — and from density, body fat.
Women measure the hip as well because female fat distribution is gluteofemoral as much as abdominal — a waist-only formula would systematically underread it. The logarithms reflect that circumference differences matter proportionally, not absolutely: 5 cm on a small frame means more than 5 cm on a large one.
The ACE categories
The American Council on Exercise ranges are the most widely used interpretation scale. Note that they differ substantially by sex — women physiologically carry more essential fat:
Category
Men
Women
Essential fat
2 – 5%
10 – 13%
Athletes
6 – 13%
14 – 20%
Fitness
14 – 17%
21 – 24%
Average
18 – 24%
25 – 31%
Obese
25%+
32%+
Essential fat is a floor, not a target. It cushions organs, insulates nerves and drives hormone production; sustained levels near it impair immunity, recovery and — especially in women — reproductive health. The leanest sustainable look for most people lives in the athlete range, and even physique competitors only visit the bottom of it briefly.
Measuring correctly
The formula is only as good as the tape work. The protocol that the military itself uses:
Neck — just below the larynx, tape sloping slightly downward to the front. Do not flare the neck.
Waist — men at the navel; women at the narrowest point of the torso. Measure at the end of a normal exhale, tape level with the floor.
Hip (women) — at the widest point of the buttocks, viewed from the side.
Snug but not compressing, on bare skin, same time of day — morning before eating is most repeatable. Take each measurement two or three times and average.
How it compares to DEXA — and to BMI
Validation studies put the Navy method within about ±3–4% of DEXA for most adults, with the largest errors at the extremes: very lean, very muscular, or unusually distributed. That sounds loose, but it is far better than the alternatives at the same price. The BMI-derived estimate shown in the calculator (the Deurenberg equation) works from weight, height, age and sex alone and carries roughly ±5% — it is there as a sanity check, and a visible demonstration of why circumference beats the scale. If the two disagree sharply, believe the tape: it can at least see where your mass sits, which BMI cannot.
Where precision genuinely matters — clinical decisions, physique-sport prep — a DEXA scan is the practical reference. For everyone else, a monthly tape reading under consistent conditions tracks fat loss and muscle gain surprisingly well, and feeds directly into related numbers: your lean body mass and the Katch-McArdle version of BMR both come straight from it. If you are being taped against a military standard, the Army now uses a different, one-site protocol — see the Army body fat calculator.
Frequently asked questions
How accurate is the Navy body fat method?+
Against DEXA or underwater weighing, the Navy tape method typically lands within ±3–4% for most people. It reads least accurately at the extremes — very lean athletes often measure a little high, and it can misread people with unusual fat distribution. Its real strength is tracking: measured consistently, the trend is trustworthy even when the absolute number is a few points off.
What is a good body fat percentage?+
By the ACE categories, the fitness range is roughly 14–17% for men and 21–24% for women, with athletes typically at 6–13% and 14–20% respectively. Averages run higher — 18–24% for men and 25–31% for women. Essential fat (2–5% men, 10–13% women) is a physiological floor, not a goal; going below it impairs hormones and health.
Where exactly do I measure for the Navy method?+
Neck: just below the larynx (Adam's apple), tape sloping slightly down to the front. Waist: men measure at the navel, women at the narrowest point of the torso. Women also measure hips at the widest point. Keep the tape level and snug without compressing the skin, measure on bare skin after exhaling normally, and take each measurement two or three times.
Why does my body fat differ from what my smart scale says?+
Smart scales use bioelectrical impedance, which is heavily affected by hydration — readings can swing several points between morning and evening on the same day. The tape method measures geometry instead, so it is immune to water shifts but blind to some distribution patterns. Neither matches a DEXA scan exactly; both are useful if you measure under consistent conditions.
Can I lose fat from just my waist by measuring there?+
No — spot reduction does not work. Fat loss comes from an overall calorie deficit, and where it leaves first is genetic. The waist measurement is still valuable because visceral fat responds reliably to total fat loss, so a shrinking waist is one of the best simple signals that a diet is working.
Is the Navy method better than BMI?+
For individuals, usually yes. BMI only relates weight to height and cannot tell muscle from fat, while the Navy method estimates composition directly from where you carry circumference. A muscular person often reads 'overweight' by BMI while taping at a healthy body fat. BMI remains useful as a fast population screen — this method answers the question BMI is guessing at.