Skinfold Body Fat (7-Site) Calculator

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.

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.