Jackson-Pollock 7-Site Skinfold Calculator
Calculate body-fat percentage from seven caliper skinfolds (chest, midaxillary, triceps, subscapular, abdomen, suprailiac, thigh) with the Jackson-Pollock 7-site equations and the Siri and Brozek formulas.
How it works
S = sum of 7 skinfolds (mm) · Men: BD = 1.112 − 0.00043499·S + 0.00000055·S² − 0.00028826·age · Women: BD = 1.097 − 0.00046971·S + 0.00000056·S² − 0.00012828·age · Siri: %BF = 495 ÷ BD − 450 · Brozek: %BF = 457 ÷ BD − 414.2
The Jackson-Pollock 7-site equations (Jackson & Pollock 1978 for men; Jackson, Pollock & Ward 1980 for women) predict body density from the sum of seven skinfolds, which is then converted to body-fat percentage with the Siri or Brozek equation. Using seven sites spreads measurement error across the body and makes the estimate less sensitive to where an individual stores fat than 3-site methods. Measure on the right side, take each site two or three times, and use the average.
Worked example
A 30-year-old man, 80 kg, with skinfolds of 10, 12, 10, 14, 20, 14 and 15 mm (sum 95 mm): BD = 1.112 − 0.04132 + 0.00496 − 0.00865 = 1.0670 g/cm³, so Siri body fat = 495 ÷ 1.0670 − 450 = 13.9% (Brozek 14.1%) — the ACE Athletes category (6–13%), with 11.1 kg of fat and 68.9 kg of lean mass.
Sources: Jackson AS, Pollock ML. Generalized equations for predicting body density of men. Br J Nutr 1978 · Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Med Sci Sports Exerc 1980
Frequently asked questions
Where are the 7 skinfold sites?
Chest (diagonal, between armpit and nipple), midaxillary (vertical, on the mid-armpit line at the level of the sternum tip), triceps (vertical, back of the upper arm), subscapular (diagonal, below the shoulder blade), abdomen (vertical, 2 cm beside the navel), suprailiac (diagonal, above the hip bone) and thigh (vertical, front of the thigh midway between hip and knee).
Is the 7-site more accurate than the 3-site?
Slightly, on average — both have a standard error of about 3–4% body fat against underwater weighing, but seven sites reduce the effect of unusual fat distribution. Consistency of the measurer matters more than the method.
Siri or Brozek — which should I use?
Both convert density to fat percentage and differ by less than one point for most people. Siri (1961) is the most widely used; Brozek (1963) reads slightly lower at high body fat.
What calipers do I need?
A spring caliper with constant pressure (about 10 g/mm²), such as Harpenden or Lange, gives the most reliable readings. Cheap plastic calipers work for tracking change if you always use the same one.
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This calculator gives an estimate for general fitness and education only. It is not a diagnosis — results from field tests and prediction equations can differ from laboratory measurements, so talk to a doctor or qualified exercise professional before acting on them.