Skinfold Body Fat Calculator (Calipers)
Estimate body fat from caliper skinfolds with the Jackson–Pollock 3-site and 7-site equations or the Durnin–Womersley 4-site equations, converting body density to body fat with the Siri or Brozek formula.
How to Use
- Choose the method: Jackson–Pollock 3-site (quickest), Jackson–Pollock 7-site, or Durnin–Womersley 4-site.
- Pick man or woman and enter the age; the sites change with the method and, for the 3-site test, with sex.
- Take each skinfold on the right side of the body, as shown in the figure, and type the reading in millimetres. Taking each site two or three times and averaging helps.
- Choose Siri or Brozek for turning body density into body fat, and add your weight (kg, lb or stone) if you want fat and lean mass.
- Read body fat, the ACE category and the sum of skinfolds; Show Work lists the density equation and both conversions.
Worked Example
A man of 30, Jackson–Pollock 3-site. Chest 12, abdomen 20 and thigh 15 mm add up to 47 mm. Body density = 1.10938 − 0.0008267 × 47 + 0.0000016 × 47² − 0.0002574 × 30 = 1.06634 g/cm³. Siri: (4.95 ÷ 1.06634 − 4.50) × 100 = 14.2% (Brozek gives 14.4%). At 80 kg that is 11.4 kg of fat, in the ACE fitness range for men (14–17%).
A woman of 35, Durnin–Womersley. Biceps 8, triceps 20, subscapular 16 and suprailiac 15 mm make 59 mm. For women aged 30–39 the table gives c = 1.1423 and m = 0.0632, so density = 1.1423 − 0.0632 × log₁₀ 59 = 1.03038 g/cm³ and body fat is 30.4% by Siri.
The common mistake: using the men’s equation for a woman. A 28-year-old woman’s triceps, suprailiac and thigh (56 mm) in the men’s 3-site equation give 16.6%. Her own equation, from Jackson, Pollock and Ward, gives 22.7%. The sites and the coefficients both differ between the sexes.
Show Work
Formulas
Durnin–Womersley c and m, all four skinfolds (1974, table 5). Men 17–19: 1.1620, 0.0630; 20–29: 1.1631, 0.0632; 30–39: 1.1422, 0.0544; 40–49: 1.1620, 0.0700; 50+: 1.1715, 0.0779. Women 16–19: 1.1549, 0.0678; 20–29: 1.1599, 0.0717; 30–39: 1.1423, 0.0632; 40–49: 1.1333, 0.0612; 50+: 1.1339, 0.0645.
Where to Pinch, and Where the Equations Come From
Taking the folds. Pinch skin and the fat under it between thumb and finger, lift it away from the muscle, put the caliper jaws on the fold beside your fingers and read once the dial settles, which for most sites takes 2 to 3 seconds. Durnin and Womersley measured on the right side, standing relaxed, to the nearest millimetre (half a millimetre for thin folds), with Harpenden or Lange calipers. The sites, as described in the anthropometry manuals: chest — a diagonal fold over the outer edge of the chest muscle, between the front of the armpit and the nipple; midaxillary — a vertical fold on the line down from the middle of the armpit, level with the bottom of the breastbone; triceps — a vertical fold on the back of the upper arm, halfway between the shoulder tip and the elbow; subscapular — a diagonal fold just below the lower tip of the shoulder blade, about 45°; abdomen — a vertical fold about 2 cm to the side of the navel; suprailiac — a fold just above the hip bone in the midaxillary line; thigh — a vertical fold on the front of the thigh, halfway between the hip crease and the top of the kneecap; biceps — a vertical fold on the front of the upper arm, over the middle of the biceps.
The equations. In 1974 J. V. G. A. Durnin and J. Womersley, at the Institute of Physiology in Glasgow, published equations from the underwater weighing of 481 people (209 men and 272 women) aged 16 to 72, with a separate line for each age band because the link between skinfolds and total fat changes with age. A. S. Jackson and M. L. Pollock then built “generalized” equations that put age into a single formula: in 1978 for 403 men aged 18 to 61, measured at Wake Forest University and the Institute for Aerobics Research in Dallas, and in 1980, with A. Ward, for women aged 18 to 55. Both pairs of authors turned body density into fat with W. E. Siri’s formula; Brozek, Grande, Anderson and Keys published their alternative in 1963.
The ACE categories (essential fat, athletes, fitness, average, obese) are the American Council on Exercise’s general body-fat ranges, the same ones the Body Fat Calculator uses.
About This Tool
This calculator turns caliper skinfolds into body density with the Jackson–Pollock 3-site or 7-site equations (separate for men and women) or the Durnin–Womersley 4-site equations (by sex and age band), then into body fat by Siri or Brozek, and shows fat and lean mass if you add your weight. The figure marks where to pinch for the method you choose and the direction of each fold, and places the result on the ACE scale. Every coefficient was checked against the original papers or, for the 1980 women’s equations, against published papers that reproduce them.
Skinfolds estimate only the fat under the skin and infer the rest, so a single reading is an estimate within a few percentage points; it is most useful for following change over time. For general information only — not medical advice. Talk to a doctor or other qualified professional about your own health.
Everything runs in your browser; nothing you enter is sent anywhere.
Related tools: Body Fat Calculator, Lean Body Mass & FFMI Calculator, and BMI Calculator.
Frequently Asked Questions
Which skinfold sites does the 3-site test use?
For men, Jackson and Pollock (1978) use the chest, abdomen and thigh; for women, Jackson, Pollock and Ward (1980) use the triceps, suprailiac and thigh. A man of 30 with 12, 20 and 15 mm (47 mm in all) has a body density of 1.06634 g/cm³, which is 14.2% body fat by Siri.
What is the difference between the Siri and Brozek equations?
Both turn body density into body fat, assuming fixed densities for fat and lean tissue. Siri is %fat = (4.95 ÷ D − 4.50) × 100; Brozek is (4.570 ÷ D − 4.142) × 100. They agree within about a point for most people: at a density of 1.03 they give 30.6% and 29.5%, at 1.08 they give 8.3% and 9.0%.
Why does age change the result when the skinfolds are the same?
The relationship between the fat under the skin and total body fat changes with age, so the equations include it. In the men’s 3-site equation, 47 mm gives 13.1% at age 20, 14.2% at 30, 16.5% at 50 and 17.6% at 60.
Which method should I use?
Use the one the person or programme you compare with uses, and stick to it. The 3-site tests are quick; the 7-site tests average more of the body; Durnin–Womersley needs only arm and trunk sites and has its own equation for each age band (for example women 30–39: density = 1.1423 − 0.0632 × log₁₀ of the sum).
How accurate are skinfold calipers?
The Jackson–Pollock equations were fitted to underwater weighing with a standard error of about 0.008 g/cm³ of body density, roughly 3.4–3.9 percentage points of body fat. The tester matters more than the formula, so track change with the same sites, the same calipers and the same person measuring.
How do I use the Skinfold Body Fat Calculator (Calipers)?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
Gym assessments
A trainer measures a 30-year-old man at 12, 20 and 15 mm (chest, abdomen, thigh): 14.2% body fat, 11.4 kg of fat at 80 kg, ACE fitness range.
Women’s 3-site test
A 28-year-old woman with triceps 18, suprailiac 14 and thigh 24 mm (56 mm) has a density of 1.0472 and 22.7% body fat.
Durnin–Womersley in clinics
A 35-year-old woman with biceps 8, triceps 20, subscapular 16 and suprailiac 15 mm (59 mm) is 30.4% body fat, 19.5 kg at 64 kg.
Tracking a training block
Because one equation and one tester are used throughout, a fall in the 7-site sum from 131 to 110 mm shows real fat loss even if body weight barely moves.
Coursework and labs
Show Work prints the density equation with every coefficient, so a student can check a 7-site result of 1.05148 g/cm³ and 20.8% by hand.
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