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Just below the larynx, tape sloping slightly down at the front.
At the narrowest point of the torso.
At the widest point, feet together.
28.7%
Average, 25–31% on the ACE scale for women
An estimate, not medical advice. Both methods predict body fat from proxies rather than measuring it: against underwater weighing the tape method lands within roughly 3–4 percentage points, and a caliper reading depends on pinching the same spot the same way every time. A single reading is not worth much. The change in your own reading, measured the same way on the same day of the week, is worth a great deal.
The tape method is Hodgdon and Beckett’s 1984 circumference equations, still the basis of the US Navy’s own assessment; the caliper method is Jackson and Pollock’s three-site equations (men 1978, women 1980) converted through Siri’s density formula. Both were fitted separately on male and female bodies, and neither has a published form for anyone else, which is why the choice above is the one the equations offer rather than the one a form should. Jackson-Pollock was validated on ages 18–61 for men and 18–55 for women; outside that it is extrapolating.
Weight tells you how much of you there is. Body composition tells you what it is made of, and that is the part that changes when training works. Neither method here measures fat directly — that takes hydrostatic weighing or a DEXA scan — but both predict it from something you can measure at home, and both were validated against the laboratory methods they stand in for.
The tape route is the US Navy circumference method, published by Hodgdon and Beckett in 1984 and still the basis of the Navy’s own assessment. The caliper route is Jackson and Pollock’s three-site equations, which turn a sum of skinfolds into body density and then into a percentage through Siri’s formula.
A woman 165 cm tall with a 32 cm neck, a 74 cm waist and 98 cm hips comes out at 28.7% — the average band on the American Council on Exercise chart. At 65 kg that splits into 18.7 kg of fat and 46.3 kg of everything else. Widen the waist by 5 cm alone and the estimate moves to 31.2%, which is why it matters so much where the tape sits.
A man 180 cm tall with a 38 cm neck and a 91 cm abdomen reads 20.6%, giving 16.9 kg of fat and 65.1 kg of lean mass at 82 kg. The same man measured with calipers at a 45 mm three-site sum reads 13.8% instead — a seven point gap between two published methods on one body, which is the honest scale of the uncertainty here.
The neck is measured just below the larynx, tape sloping slightly downward at the front. For men the second measurement is the abdomen at the navel, level all the way round and read after breathing out. For women it is the natural waist at its narrowest, plus the hips at their widest with the feet together.
Measuring somewhere else is the largest source of error in the method, larger than the equation’s own. Pull the tape snug without compressing, keep it horizontal, and take repeat readings at the same time of day — abdominal girth varies by a couple of centimetres between morning and evening.
Against underwater weighing the circumference method lands within roughly three to four percentage points for most people, and it is least reliable at the extremes: very lean and very heavy bodies both drift. Caliper accuracy depends on the person holding them — a trained assessor is repeatable to about a point, an untrained one is not.
So read the trend rather than the absolute figure. Measured the same way, at the same time, by the same person, a drop of two points over eight weeks is real information even if the starting number was off by three.
The American Council on Exercise puts essential fat at 2–5% for men and 10–13% for women — the amount required for organ function, nerve insulation and hormone production. Women who drop near that floor commonly stop menstruating and lose bone density. Athletic ranges sit well above it, at 6–13% and 14–20%.
Bathroom scales estimate composition by passing a small current through your body and inferring fat from the resistance. That reading moves with hydration, food, exercise and skin temperature, so it can swing several points across a single day. Being electrical does not make it more scientific than a tape measure.
Use the tape if you have no calipers or nobody to hold them, which covers most people. Use calipers if someone experienced is taking the readings, because a well-taken skinfold carries more information than a girth does. Whichever you pick, keep using it — switching methods invents a change that did not happen.
No. Both were fitted separately on male and female bodies and neither has a published form for anyone outside that split. Jackson-Pollock was validated on ages 18 to 61 for men and 18 to 55 for women, and the circumference method was built on a military population fitter than average.