Body composition · 6 min read
Body Fat Caliper Calculator: The Jackson-Pollock 3-Site Method Explained
A skinfold caliper is one of the cheapest and most portable ways to estimate body fat: pinch a fold of skin and fat, read the thickness in millimeters, and plug the numbers into a formula. The most widely used version is the Jackson-Pollock 3-site method. Here is exactly how it works, the formula behind it, and how to avoid the mistakes that throw the number off.
Want to skip straight to the numbers? Use the calculators directly - the 3-site version or the more precise 7-site version.
What a caliper actually measures
A caliper does not measure body fat directly. It measures the thickness of a skinfold, a pinch of skin plus the fat directly under it, at specific sites on your body. Because fat sits in a fairly predictable ratio to skinfold thickness at the population level, researchers built regression formulas that convert a handful of skinfold measurements into an estimated body density, and from there into a body fat percentage.
The Jackson-Pollock 3-site method
Developed in 1978 (men) and 1980 (women), Jackson-Pollock uses three skinfold sites, and the sites differ by sex:
- Men: chest, abdomen, thigh
- Women: triceps, suprailiac (above the hip bone), thigh
You sum the three skinfold thicknesses (in millimeters), then apply a formula that also factors in age:
Women: Body density = 1.0994921 - 0.0009929(sum) + 0.0000023(sum²) - 0.0001392(age)
Body density then converts to body fat percentage with the Siri equation: %BF = (495 / density) - 450. This is exactly the calculation our body-fat calculator runs for you when you enter your three skinfold readings, so you never have to do the arithmetic by hand.
How to measure each site correctly
- Pinch skin and fat only, not muscle. Grasp the fold firmly between thumb and forefinger about a centimeter above where you place the caliper jaws.
- Measure on the right side of the body, the convention used in the original research, so your numbers stay comparable over time.
- Take two to three readings per site and average them; a single pinch is noisy.
- Measure at the same time of day, ideally before training or eating, since hydration and pump can shift readings by a millimeter or two.
A worked example
Male, age 30, skinfolds of 12 mm (chest), 18 mm (abdomen) and 15 mm (thigh):
Sum = 45 mm. Body density ≈ 1.10938 - (0.0008267 × 45) + (0.0000016 × 45²) - (0.0002574 × 30) ≈ 1.0662
%BF = (495 / 1.0662) - 450 ≈ 14.4%
Enter the same three numbers into the calculator and it returns this instantly, along with a category (athletic, fit, average, and so on) and the lean mass figure you can feed into a protein target.
How accurate is it, really
In trained hands, Jackson-Pollock 3-site typically lands within about 3 to 4 percent of a lab reference method like DEXA, close enough to track real change over time but not precise enough to treat any single reading as exact. Self-measurement adds more noise than a technician taking the pinch, since reaching your own back or thigh consistently is harder than it sounds. For a full comparison against tape measurements, BIA scales and DEXA, see our body fat measurement methods guide.
Common mistakes that throw the number off
- Pinching muscle along with fat, which inflates the reading. Relax the muscle and grasp only the fold that lifts away from it.
- Moving the measurement site slightly each time, which makes week-to-week comparisons meaningless. Mark or note the exact spot.
- Using cheap calipers with weak spring tension, which under-compress the fold. A basic plastic Jackson-Pollock caliper is fine; it just needs consistent pressure.
- Chasing the exact percentage instead of the trend. The real value of calipers is tracking change over weeks and months, not nailing an absolute number.
Enter your three Jackson-Pollock skinfold measurements and the calculator returns your body fat percentage, category and lean mass instantly.
Turn your skinfolds into a body fat percentage →Frequently asked questions
Do I need special calipers?
A basic plastic or metal skinfold caliper with consistent spring tension is enough; you do not need a lab-grade device for the Jackson-Pollock formula to work. Cheap calipers cost very little and are widely available online.
Is Jackson-Pollock accurate?
It typically lands within about 3 to 4 percent of a DEXA scan when measured by a trained technician, which is good enough to track meaningful change over time. Self-measurement is noisier, so focus on the trend across weeks rather than any single reading.
Is 3-site or 7-site better?
The 7-site protocol adds more measurement points and can be marginally more accurate in research settings, but it takes longer and is harder to do consistently on yourself. For most people tracking progress at home, 3-site is the practical choice.
Where exactly do I measure for men versus women?
Men measure chest, abdomen and thigh. Women measure triceps, suprailiac (just above the hip bone) and thigh. Using the wrong sites for your sex will give you a meaningless number, since the formulas are sex-specific.
References
- Jackson AS, Pollock ML. Generalized equations for predicting body density of men. Br J Nutr. 1978;40(3):497-504. doi:10.1079/BJN19780152
- Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Med Sci Sports Exerc. 1980;12(3):175-181.
- Siri WE. Body composition from fluid spaces and density: analysis of methods. 1961. Reprinted in Nutrition. 1993;9(5):480-491.