Estimate body fat percentage using the Jackson-Pollock 3-site skinfold method. Enter caliper measurements from three body sites for an accurate body composition estimate.
The Jackson-Pollock 3-site skinfold test is one of the most popular field methods for estimating body fat percentage. Using a skinfold caliper, you measure fat thickness at three specific body sites, then apply validated equations to estimate body density and body fat.
The measurement sites differ by sex. Men: chest (pectoral), abdomen, and thigh. Women: triceps, suprailiac (hip), and thigh. These sites were selected based on regression analysis to best predict total body fat with the fewest measurements.
First published in 1985 by Jackson and Pollock, the 3-site formula is widely used in personal training, sports science, and military fitness testing. It's a good balance between accuracy and practicality. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process. This tool handles all the complex arithmetic so you can focus on interpreting results and making informed decisions based on accurate data.
The 3-site skinfold test is faster than the 7-site version while still achieving good accuracy (±3.5% vs DEXA). Skinfold calipers cost $10-30 and are portable. With practice, the test takes under 5 minutes and provides more information than BMI about actual body composition. Having a precise figure at your fingertips empowers better planning and more confident decisions.
Men: Body Density = 1.10938 − 0.0008267 × S + 0.0000016 × S² − 0.0002574 × age Women: Body Density = 1.0994921 − 0.0009929 × S + 0.0000023 × S² − 0.0001392 × age S = sum of 3 skinfolds (mm) Body Fat % = (495 / Body Density) − 450 (Siri equation)
Result: Sum: 47 mm | Density: 1.0557 | Body Fat: 18.9% | Fat Mass: 15.1 kg | Lean: 64.9 kg
Sum of skinfolds S = 12 + 20 + 15 = 47 mm. Body Density = 1.10938 − 0.0008267 × 47 + 0.0000016 × 47² − 0.0002574 × 30 = 1.0557. Body Fat % = (495 / 1.0557) − 450 = 18.9%. At 80 kg: fat mass = 15.1 kg, lean mass = 64.9 kg.
The 3-site test is faster and easier, while the 7-site test captures more detail across the body. In practice, the 3-site formula is within 1% of the 7-site for most people. The 7-site is preferred in research settings and when you need maximum accuracy. The 3-site is better for frequent tracking and when time is limited.
Chest (men): diagonal fold, midway between the anterior axillary line and nipple. Abdomen (men): vertical fold, 2 cm to the right of the umbilicus. Thigh (both): vertical fold on the anterior midline of the thigh, midway between proximal border of the patella and inguinal crease. Triceps (women): vertical fold on the posterior midline of the upper arm, midway between acromion and olecranon. Suprailiac (women): diagonal fold, above the iliac crest at the anterior axillary line.
Men measure chest (pectoral, diagonal fold midway between armpit and nipple), abdomen (vertical fold 1 inch to the right of the navel), and thigh (vertical fold midway between hip and knee on the front of the thigh). Women measure triceps (vertical fold on the back of the upper arm), suprailiac (diagonal fold above the hip bone), and thigh (same as men). These specific sites were validated by Jackson and Pollock in their original research.
The Jackson-Pollock 3-site formula has a standard error of estimate of about 3.5% body fat compared to hydrostatic weighing. In practice, with a skilled tester, you can expect results within ±3-4% of DEXA. The key factors affecting accuracy are tester experience, consistent technique, and caliper quality. Repeated measurements by the same tester improve reliability.
For clinical accuracy, Harpenden or Lange calipers ($200-400) are the standard. For personal use, Slim Guide ($25) or AccuMeasure ($10) calipers provide acceptable accuracy. The most important factor is consistent jaw pressure (10 g/mm²) and reading technique. Cheap plastic calipers from Amazon vary significantly in jaw pressure and should be avoided for tracking purposes.
Body density changes with age independently of skinfold thickness. As people age, internal (visceral) fat increases even if subcutaneous fat stays the same. Bone density also decreases with age, affecting overall body density. The age correction term accounts for these changes, making the formula more accurate across different age groups.
The Siri equation converts body density to body fat percentage: BF% = (495 / density) − 450. It assumes fat density = 0.900 g/cm³ and fat-free mass density = 1.100 g/cm³. An alternative, the Brozek equation ((457 / density) − 414.2), gives slightly different results. The Siri equation is the standard in Jackson-Pollock methodology. Both assume a two-compartment model (fat vs. fat-free mass).
Absolutely — this is one of its best uses. Even if the absolute body fat estimate has some error, tracking changes over time is very reliable when the same person measures with the same technique. The sum of skinfolds alone (without plugging into the formula) is an excellent progress metric. A decrease from 50 mm to 40 mm clearly indicates fat loss regardless of the converted percentage.