Body Fat (3-Site Skinfold, Jackson-Pollock) Calculator
Convert three caliper skinfold measurements into body-fat percentage with the Jackson-Pollock 3-site equation and the Siri conversion.
How it works
Sum S = fold1+fold2+fold3 · Men: BD = 1.10938 − 0.0008267·S + 0.0000016·S² − 0.0002574·age · Women: BD = 1.0994921 − 0.0009929·S + 0.0000023·S² − 0.0001392·age · %BF = 495 ÷ BD − 450 (Siri)
Skinfold calipers pinch the subcutaneous fat layer at standard sites; the Jackson-Pollock 3-site equation turns the total thickness into body density, which the Siri equation converts to a fat percentage. The age term corrects for fat that shifts from under the skin to around the organs as we age. Careful, repeatable pinches at the correct sites are what make it accurate.
Worked example
A 30-year-old man with chest 15 mm, abdomen 20 mm and thigh 18 mm has a sum of 53 mm. Body density = 1.10938 − 0.0008267·53 + 0.0000016·53² − 0.0002574·30 ≈ 1.0624, so body fat = 495 ÷ 1.0624 − 450 ≈ 16.0%.
Sources: Jackson & Pollock skinfold equations
Frequently asked questions
Which sites do men and women use?
Men measure chest, abdomen and thigh; women measure triceps, suprailiac and thigh. Using the wrong sites for your sex invalidates the equation, because the coefficients were derived for those specific folds.
Why is age part of the formula?
At the same skinfold thickness, older adults tend to carry more internal (visceral) fat that calipers cannot pinch. The age term compensates so the estimate stays accurate across the adult lifespan.
How do I improve accuracy?
Pinch on the right side of the body, take each fold two or three times and average, measure before exercise (not after, when skin is engorged), and have the same person do the measuring each time.
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Educational estimate only — not medical advice, diagnosis or treatment. Consult a qualified clinician for health decisions.