Estimate body fat percentage with the Jackson-Pollock 7-site skinfold method. The most comprehensive caliper test using chest, midaxillary, triceps, subscapular, abdomen, suprailiac, and thigh.
The Jackson-Pollock 7-site skinfold test is the gold standard of caliper-based body fat estimation. By measuring seven locations across the body, it captures a more complete picture of subcutaneous fat distribution than the 3-site version.
All seven sites are measured for both men and women: chest, midaxillary, triceps, subscapular, abdomen, suprailiac, and thigh. The sum is plugged into a sex-specific equation that yields body density, which is then converted to body fat percentage via the Siri equation.
Published by Jackson and Pollock (1978 for men, 1980 with Ward for women), the 7-site formula is widely used in exercise science research, university labs, and advanced fitness testing protocols. 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 7-site formula provides the most comprehensive caliper-based body fat estimate. By sampling more sites, it reduces the impact of any single measurement error and captures regional fat distribution patterns that the 3-site test might miss. It's the preferred method in research and professional sports settings. Having a precise figure at your fingertips empowers better planning and more confident decisions.
Men: Density = 1.112 − 0.00043499 × S + 0.00000055 × S² − 0.00028826 × age Women: Density = 1.097 − 0.00046971 × S + 0.00000056 × S² − 0.00012828 × age S = sum of 7 skinfolds (mm) Body Fat % = (495 / Density) − 450 (Siri equation)
Result: Sum: 81 mm | Density: 1.0649 | Body Fat: 14.7% | Fat: 12.1 kg | Lean: 69.9 kg
Sum S = 8 + 10 + 9 + 12 + 18 + 10 + 14 = 81 mm. Density = 1.112 − 0.00043499 × 81 + 0.00000055 × 81² − 0.00028826 × 28 = 1.0649. BF% = (495 / 1.0649) − 450 = 14.7%. At 82 kg: fat = 12.1 kg, lean = 69.9 kg. This places him in the "Fitness" category.
The original validation studies included 308 men (Jackson & Pollock, 1978) and 249 women (Jackson, Pollock & Ward, 1980). Participants ranged from 18-61 years old. Body density was measured via hydrostatic (underwater) weighing, then regression equations were derived. The equations have been cross-validated in multiple populations and remain the standard after 45+ years.
Choose the 7-site test when: you're doing a baseline assessment, accuracy matters more than speed, you have an experienced tester, or you want site-specific fat distribution data. Choose the 3-site test when: time is limited, self-measuring, or tracking frequent progress checks (weekly).
Chest: diagonal fold between armpit and nipple. Midaxillary: vertical fold on the midaxillary line at xiphoid (breastbone) level. Triceps: vertical fold on the back of the upper arm, halfway between shoulder and elbow. Subscapular: diagonal fold 1-2 cm below the inferior angle of the scapula. Abdomen: vertical fold 2 cm right of the navel. Suprailiac: diagonal fold above the iliac crest at the anterior axillary line. Thigh: vertical fold on the front of the thigh, midway between hip and knee.
In most studies, the difference is small: the 7-site has a standard error of estimate of about 3.4% vs. 3.5% for the 3-site. However, the 7-site test is more robust to individual measurement errors because no single site carries disproportionate weight. It also better captures unusual fat distribution patterns. For most people, the practical difference is minimal.
Absolutely. The sum of 7 skinfolds (in mm) is itself an excellent metric for tracking body composition changes. A decrease in the total sum reliably indicates fat loss, regardless of the formula-calculated percentage. Many strength coaches track the raw sum and individual site measurements over time for a detailed picture of where fat is being lost.
The Siri equation (BF% = 495/density − 450) converts body density to body fat percentage using a two-compartment model. It assumes fat tissue has a density of 0.900 g/cm³ and fat-free tissue 1.100 g/cm³. It was published by William Siri in 1961 and is the standard conversion used with Jackson-Pollock equations. For populations with very different bone density (e.g., elderly, some ethnicities), the Brozek equation may be more appropriate.
Realistically, yes. The subscapular (below shoulder blade) and midaxillary sites are very difficult to measure on yourself accurately. While chest, abdomen, suprailiac, triceps, and thigh can be self-measured with practice, having a trained partner or professional ensures better accuracy and repeatability, especially for the hard-to-reach sites.
Men and women store fat differently due to hormonal influences. Women have higher essential fat (for reproductive function), more subcutaneous fat in the lower body, and different relationships between skinfold thickness and total body fat. The separate equations account for these sex-specific fat distribution patterns to produce more accurate estimates for each sex.