About the Skinfold Body Fat Calculator
This skinfold body fat calculator converts caliper measurements into a body fat percentage using the three most widely used research equations: the Jackson-Pollock 3-site and 7-site formulas and the Durnin-Womersley 4-site formula. Pick a method, enter your sex, age and the skinfold thickness at each site in millimetres, and it estimates body density, body fat percentage, and — if you add your weight — fat mass and lean mass.
Each equation predicts body density from the sum of skinfolds and age, and the Siri equation converts density to body fat. Jackson-Pollock 3-site uses chest, abdomen and thigh for men and triceps, suprailiac and thigh for women; the 7-site version adds the remaining trunk sites; Durnin-Womersley uses biceps, triceps, subscapular and suprailiac with age-specific constants.
Skinfolds are a practical choice for coaches, personal trainers and anyone tracking changes over time with an inexpensive caliper. Accuracy depends heavily on technique: measure on the right side of the body, take each site two or three times and average, and keep the same tester and method from one test to the next. Expect an error of a few percentage points against laboratory methods, and focus on the trend rather than any single reading.
With the default inputs, the body fat is 17.9%. Change any value above to recalculate instantly.
How to use the skinfold body fat calculator
- 1Choose an equation: 3-site for speed, 7-site for more detail, or Durnin-Womersley 4-site.
- 2Select your sex and enter your age (and weight if you want fat and lean mass).
- 3Pinch each site on the right side of the body, apply the caliper 1 cm away from your fingers and read after about 2 seconds.
- 4Take two or three readings per site, average them and enter the values in millimetres.
- 5Read your body fat % and retest in the same way every few weeks to track the trend.
Formula and method
All three methods first estimate body density D from the sum of skinfolds S (mm). The Jackson-Pollock 7-site equations are D = 1.112 − 0.00043499·S + 0.00000055·S² − 0.00028826·age for men and D = 1.097 − 0.00046971·S + 0.00000056·S² − 0.00012828·age for women. The Durnin-Womersley constants c and m depend on sex and age band: men 1.1620/0.0630 (17–19), 1.1631/0.0632 (20–29), 1.1422/0.0544 (30–39), 1.1620/0.0700 (40–49), 1.1715/0.0779 (50+); women 1.1549/0.0678, 1.1599/0.0717, 1.1423/0.0632, 1.1333/0.0612, 1.1339/0.0645.
Density is converted to body fat with the Siri two-compartment equation, which assumes fat has a density of 0.9 g/cm³ and lean tissue 1.1 g/cm³. Fat mass is weight × body fat %, and lean mass is the remainder. Categories follow the commonly used American Council on Exercise ranges.
- S
- Sum of skinfolds for the chosen method (mm)
- D
- Estimated body density (g/cm³)
- c, m
- Durnin-Womersley constants for your sex and age band
Worked examples
Man, 30, JP 3-site: chest 20, abdomen 25, thigh 15 mm
S = 60 mm, so D = 1.10938 − 0.0008267 × 60 + 0.0000016 × 3600 − 0.0002574 × 30 = 1.05782. Siri gives 495 ÷ 1.05782 − 450 = 17.9% body fat — about 14.4 kg of fat at 80 kg.
Woman, 28, JP 3-site: triceps 18, suprailiac 15, thigh 25 mm
S = 58 mm: D = 1.0994921 − 0.0009929 × 58 + 0.0000023 × 3364 − 0.0001392 × 28 = 1.04574, which is 23.3% body fat — in the fitness range for women.
Man, 40, JP 7-site totalling 103 mm
The seven sites (12 + 15 + 10 + 14 + 22 + 14 + 16) sum to 103 mm. D = 1.112 − 0.00043499 × 103 + 0.00000055 × 10609 − 0.00028826 × 40 = 1.0615, or 16.3% body fat.
Man, 45, Durnin-Womersley 4-site totalling 45 mm
Biceps 6 + triceps 12 + subscapular 15 + suprailiac 12 = 45 mm. For men aged 40–49, D = 1.1620 − 0.0700 × log10(45) = 1.04628, giving 23.1% body fat.
Woman, 25, Durnin-Womersley 4-site
The four sites sum to 52 mm. For women aged 20–29, D = 1.1599 − 0.0717 × log10(52) = 1.03686, which is 27.4% body fat.
Frequently asked questions
How accurate are skinfold calipers?+
With a trained tester and good technique, skinfold equations typically estimate body fat within about 3–4 percentage points of laboratory methods for most people. Errors are larger for very lean or very obese people and when measurement technique varies.
Is the 3-site or 7-site Jackson-Pollock more accurate?+
The 7-site formula samples more of the body and is slightly less sensitive to unusual fat distribution, but in the original studies both had similar accuracy. The 3-site version is quicker and easier to repeat consistently, which matters most for tracking change.
Which side of the body should I measure?+
The standard protocols, including the American College of Sports Medicine’s, use the right side of the body. Mark each site, take at least two measurements per site and re-measure if readings differ by more than 1–2 mm.
Why does my result differ between methods?+
Each equation was developed on a different group of people using different sites, so they weight upper-body, abdominal and leg fat differently. Pick one method and stay with it so that changes reflect your body rather than the formula.
What is the Siri equation?+
The Siri equation, body fat % = 495 ÷ density − 450, converts body density into fat percentage by assuming fat tissue has a density of 0.9 g/cm³ and fat-free tissue 1.1 g/cm³. It is the standard conversion for skinfold and underwater weighing results.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.