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Skinfold Body Fat (7-Site) Calculator

Enter your seven skinfold measurements to get your body density and body fat percentage.

How it is calculated

The tool adds seven caliper readings in millimetres (chest, midaxillary, triceps, subscapular, abdominal, suprailiac, thigh) into one sum S and estimates body density with the Jackson-Pollock 7-site equation. For men: density = 1.112 − 0.00043499 S + 0.00000055 S2 − 0.00028826 × age. For women: density = 1.097 − 0.00046971 S + 0.00000056 S2 − 0.00012828 × age. Density in g/cm³ then goes into the Siri equation, body fat % = 495 / density − 450. A negative value is shown as 0 %. Every site must have a reading above zero and no larger than 80 mm, and age must be 18 to 120 years; otherwise there is no result. Any sex setting other than female is treated as male. The equation fits typical skinfold sums, not extreme ones.

Worked example

A 30-year-old man with readings of 12, 14, 13, 15, 22, 16 and 15 mm. Step 1: sum S = 107 mm. Step 2: density = 1.112 − 0.00043499 × 107 + 0.00000055 × 1072 − 0.00028826 × 30 = 1.06311 g/cm³. Step 3: body fat = 495 / 1.06311 − 450 = 465.62 − 450 = 15.62%. For a woman of the same age with the same readings the equation gives a density of 1.04930 and 21.74%.

Try this example →

Common mistakes

  • Pinching the wrong spot, or a different side of the body between sessions. The equation assumes the standard sites, measured the same way, usually on the right side.
  • Entering centimetres instead of millimetres. The equation is built for millimetres, so seven folds of 1.2 to 2.2 are treated as millimetres and give an absurdly low result (about 3.9 % in a test).
  • Reading the caliper at a different moment after the pinch each time. Taking each value consistently, ideally the average of two or three tries, keeps the sum repeatable.
  • Leaving the sex setting at its default for a woman. The same readings give very different results (15.62 % against 21.74 % in the example).
  • Comparing the result with a scale or an underwater test and expecting identical numbers. This is an estimate with a margin of error of several percentage points.

Sources

About this calculator

The Jackson-Pollock 7-site skinfold method estimates body density by measuring skinfold thickness with calipers at seven standardized points — chest, midaxillary, triceps, subscapular, abdomen, suprailiac and thigh — then plugging the sum into a regression equation that differs for men and women and adjusts for age. That body density is then converted to a body fat percentage using the Siri equation, a widely used formula relating density to fat mass.

Personal trainers, strength coaches and athletes favor the 7-site method over simpler 3-site protocols or bioelectrical impedance scales because measuring more sites reduces the error introduced by any single inaccurate pinch, giving a more reproducible estimate for tracking body composition changes over weeks or months of training. It remains an estimate — actual accuracy depends heavily on measurement technique and caliper consistency — but it is inexpensive and far more informative than BMI, which cannot distinguish muscle from fat.

Your estimated body density and body fat percentage are calculated from seven skinfold measurements plus your age and sex.

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