Body composition calculator
Jackson-Pollock 7-site calculator
Body-fat percentage from seven caliper readings and your age — the full Jackson & Pollock method. Free, instant, no sign-up.
Both sexes measure the same seven sites — only the equation's coefficients change.
Seven folds give you a number — the coach gives you the plan that moves it.
What is the Jackson-Pollock 7-site method?
This is the reference version of the Jackson & Pollock generalised equations — men from Jackson & Pollock (1978), women from Jackson, Pollock & Ward (1980). The widely used three-site and four-site forms were published as shortcuts to it. Seven folds take longer, but each site carries a seventh of the total instead of a third, so one badly taken reading moves the answer far less. If you are being measured by someone else and want the most defensible skinfold number, this is the one.
How this calculator works
Chest, midaxillary, triceps, subscapular, abdomen, suprailiac and thigh are summed in millimetres, and the sum goes into an age-adjusted quadratic: for men, D = 1.112 − 0.00043499·Σ + 0.00000055·Σ² − 0.00028826·age; for women, D = 1.097 − 0.00046971·Σ + 0.00000056·Σ² − 0.00012828·age. The density is then converted with Siri's equation, 495/D − 450. Only the sum matters to the equation, not how it is distributed — but that is exactly why each individual fold has to be taken properly.
How to take the folds
All seven are measured on the right side, with the muscle underneath relaxed. Chest is diagonal, halfway between armpit and nipple; midaxillary is vertical on the midaxillary line, level with the bottom of the sternum; triceps is vertical, midway between shoulder and elbow; subscapular is diagonal, just below the bottom corner of the shoulder blade; abdomen is vertical, about 2 cm beside the navel; suprailiac is diagonal, just above the hip bone; thigh is vertical, midway between hip crease and kneecap. Pinch a centimetre away from the jaws, read two seconds after releasing, and rotate through all seven sites three times rather than taking three readings at one site in a row — the tissue compresses if you keep going back. Use the median of the three.
How to use the number
Expect a standard error of around 3.5 percentage points against hydrostatic weighing, and expect the tester to be a bigger source of variation than the maths. Keep the same tester, the same calipers and the same sites, and read the trend over months rather than the value on any one day. This is an estimate for training decisions, not a medical assessment.