Skinfold Body Fat Calculator (Jackson–Pollock 3 & 7 Site)
Turn caliper readings into body fat percentage with the Jackson–Pollock 3-site or 7-site skinfold equations, plus body density, fat mass and lean mass.
Skinfold testing estimates body fat from the thickness of pinched folds of skin and fat at standard places on the body. This calculator feeds your caliper readings into the Jackson–Pollock equations to get body density, then converts density to body fat with the Siri equation, with the Brozek version alongside. Choose the quick 3-site test or the more thorough 7-site one.
How to use this tool
- Pick your sex, age and the 3-site or 7-site method.
- Take each fold on the right side: pinch it firmly, place the caliper jaws about 1 cm from your fingers and read after 1–2 seconds.
- Measure each site two or three times and enter the average in millimetres. The 3-site test uses chest, abdomen and thigh for men, or triceps, suprailiac and thigh for women.
- Add your weight to see fat mass and lean mass.
Formula
Men, 3-site: BD = 1.10938 − 0.0008267 S + 0.0000016 S² − 0.0002574 × age
Women, 3-site: BD = 1.0994921 − 0.0009929 S + 0.0000023 S² − 0.0001392 × age
Men, 7-site: BD = 1.112 − 0.00043499 S + 0.00000055 S² − 0.00028826 × age
Women, 7-site: BD = 1.097 − 0.00046971 S + 0.00000056 S² − 0.00012828 × age
Siri: %BF = 495 ÷ BD − 450
S is the sum of the skinfolds in millimetres and BD is body density in g/cm³. Brozek’s alternative is %BF = 457 ÷ BD − 414.2. The seven sites are chest, midaxillary, triceps, subscapular, abdomen, suprailiac and thigh.
Example
A 30-year-old man measures 10 mm at the chest, 20 mm at the abdomen and 15 mm at the thigh, so S = 45 mm. Body density = 1.10938 − 0.03720 + 0.00324 − 0.00772 = 1.0677 g/cm³, and Siri gives 495 ÷ 1.0677 − 450 ≈ 13.6% body fat (Brozek: 13.8%). At 180 lb that is about 24.5 lb of fat.
Frequently asked questions
Is the 3-site or 7-site test better?
The equations use different site sums and coefficients. Seven sites do not guarantee a more accurate result for every person. Use the same measurement protocol for comparisons, and have a trained tester take sites that are difficult to reach.
Why does the calculator ask for my age?
At the same skinfold thickness, older adults tend to carry more fat inside the body, so the equations lower body density as age goes up. The original studies covered men aged 18–61 and women aged 18–55.
How accurate are skinfold calipers?
Both measurement and model error matter. The original studies compared estimates with underwater weighing and reported group-level error, not a guaranteed individual accuracy. This page limits ages to the original samples and rejects nonphysical or extreme extrapolations.
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
- Jackson and Pollock 1978 — primary paper reproduced as a BJN Citation Classic, Table 1 and equations
- Temple et al. — validation study reproducing female equations, Table 1
This tool gives an estimate for general information only. It is not financial, tax, legal or medical advice — check with a qualified professional before you rely on the result.
Last updated: 2026-10-30