Key Takeaways
- The Jackson-Pollock 3-site skinfold method uses gender-specific equations to estimate body density from three skinfold measurements, then converts to body fat percentage using the Siri equation.[1][2]
- The original validation studies found correlations of r = 0.90+ with hydrostatic (underwater) weighing, with a standard error of estimate of approximately ±3.5% body fat.[1]
- Male measurement sites are chest, abdomen, and thigh. Female sites are tricep, suprailiac, and thigh. The different sites were selected to optimize prediction accuracy for each gender.
- The Siri equation (BF% = 495 / Body Density − 450) assumes a two-compartment body model, which is most accurate for individuals with typical body composition ranges.[3]
How the Jackson-Pollock 3-Site Method Works
Developed by Jackson and Pollock (1978) for men and Jackson, Pollock, and Ward (1980) for women, these generalized equations predict body density from the sum of three skinfold measurements plus age. The equations use a quadratic term (S²) to account for the non-linear relationship between skinfold thickness and body density.
Male Body Density (Jackson & Pollock, 1978):
BD = 1.10938 − 0.0008267 × S + 0.0000016 × S² − 0.0002574 × Age
Female Body Density (Jackson, Pollock & Ward, 1980):
BD = 1.0994921 − 0.0009929 × S + 0.0000023 × S² − 0.0001392 × Age
Siri Equation:
Body Fat % = (495 / BD) − 450
Where S is the sum of three skinfold measurements in millimeters. The body density result is then converted to body fat percentage using the Siri equation.[3]
Measurement Site Guide
Proper technique is essential for reliable results. All measurements should be taken on the right side of the body using calibrated skinfold calipers. Pinch the skin firmly and measure 1–2 seconds after releasing the caliper lever.
Male Sites
| Site | Fold Direction | Location |
|---|---|---|
| Chest | Diagonal | Midway between the anterior axillary fold (front of armpit) and the nipple |
| Abdomen | Vertical | 2 cm to the right of the navel (umbilicus) |
| Thigh | Vertical | Midway between the inguinal crease (hip joint) and proximal border of the patella (kneecap) |
Female Sites
| Site | Fold Direction | Location |
|---|---|---|
| Tricep | Vertical | Posterior midline of the upper arm, midway between the acromion (shoulder) and olecranon (elbow) |
| Suprailiac | Diagonal | Just above the iliac crest on the midaxillary line (side of torso) |
| Thigh | Vertical | Midway between the inguinal crease and proximal border of the patella |
Understanding Your Results
Your body fat percentage result is classified into one of five categories using neutral labels. These provide a general reference point for personal tracking — not a clinical assessment.
For an alternative circumference-based body fat estimation method, see the US Navy Body Fat Calculator, which uses neck, waist, and hip measurements instead of skinfold calipers. You can also use the BMI Calculator for a simpler height-and-weight-based reference, though BMI does not distinguish between fat mass and lean mass.
For additional skinfold methods, compare your results with the Jackson-Pollock 4-Site, Jackson-Pollock 7-Site, Durnin-Womersley 4-Site, or Parrillo 9-Site calculators.
Accuracy and Comparison
The Jackson-Pollock 3-site equations were validated against hydrostatic weighing (the traditional gold standard) and showed strong correlations (r ≥ 0.90) with a standard error of estimate (SEE) of approximately ±3.5% body fat.[1][2] This means your true body fat percentage is likely within ±3.5% of the calculated value.
Key factors affecting accuracy include:
- Caliper quality and calibration — use spring-loaded calipers that apply consistent pressure (10 g/mm²).
- Measurement technique — take each site 2–3 times and use the average.
- Hydration status — dehydration can thin the skinfold and underestimate body fat.
- The equations were developed on predominantly young adult populations. Accuracy may decrease at extremes of age, leanness, or body size.
Limitations
The Siri equation assumes constant densities for fat tissue (0.900 g/cm³) and fat-free mass (1.100 g/cm³). This two-compartment model works well for the general population but may produce errors for individuals with very high muscle mass, very low body fat, or different bone mineral density profiles.[3]
Skinfold measurements require practice to perform consistently. Inter-tester variability can be significant — for the most reliable tracking over time, have the same person take measurements each session using the same technique.
Frequently Asked Questions
Sources & References
- Generalized equations for predicting body density of men. Jackson AS, Pollock ML. British Journal of Nutrition (1978)
- Generalized equations for predicting body density of women. Jackson AS, Pollock ML, Ward A. Medicine & Science in Sports & Exercise (1980)
- Accuracy of Siri and Brozek Equations in the Percent Body Fat Estimation in Older Adults. Ferreira-Fernandes H, Santos DA, Espiga Macedo M, Sardinha LB. Nutrition (2024)
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