Skinfold Body Fat Calculator (Jackson-Pollock 3-Site)
Estimate body fat from three skinfolds with the classic Jackson-Pollock equations and the Siri conversion - the field method used in exercise-science testing.
Results
- Body density
- 1.0683
- Jackson-Pollock 3-site equation (male)
- Estimated body fat
- 13.4%
- Siri equation from body density
- Category
- Athletes
- General population ranges (ACE-style categories)
Measurement sites
| Protocol | Sites |
|---|---|
| 3-site (men) | Chest, abdomen, thigh |
| 3-site (women) | Triceps, suprailiac, thigh |
| 7-site (both) | Chest, midaxillary, triceps, subscapular, abdomen, suprailiac, thigh |
Density conversion equations
| Equation | Formula |
|---|---|
| Siri (1956) | Body fat % = (495 / density) - 450 |
| Brozek (1963) | Body fat % = (457 / density) - 414.2 |
How it works & limitations
The equations
3-site men: density = 1.10938 - 0.0008267 x sum + 0.0000016 x sum2 - 0.0002574 x age 3-site women: density = 1.0994921 - 0.0009929 x sum + 0.0000023 x sum2 - 0.0001392 x age 7-site men: density = 1.112 - 0.00043499 x sum + 0.00000055 x sum2 - 0.00028826 x age 7-site women: density = 1.097 - 0.00046971 x sum + 0.00000056 x sum2 - 0.00012828 x age Then Siri or Brozek converts density to body fat.
Measurement technique
Grasp the skinfold about 1 cm above the site, place caliper jaws at the site, and read after about 2 seconds. Measure the right side, take each site twice and average. Same measurer, same calipers and same time of day make tracking much more reliable.
3-site vs 7-site
The 7-site equation samples more regions and is generally more accurate for individuals, while the 3-site is quicker and still widely used. Both assume the Jackson-Pollock population; very lean bodybuilders and older adults can get less accurate results.
Sources
Last updated 2026-08-13
- Jackson, A. S., & Pollock, M. L. (1978). Generalized equations for predicting body density of men. British Journal of Nutrition, 40(3), 497-504.
- Jackson, A. S., Pollock, M. L., & Ward, A. (1980). Generalized equations for predicting body density of women. Medicine & Science in Sports & Exercise, 12(3), 175-181.
- Siri, W. E. (1956). Body composition from fluid spaces and density: analysis of methods. In Techniques for Measuring Body Composition (pp. 223-244).
- Brozek, J., Grande, F., Anderson, J. T., & Keys, A. (1963). Densitometric analysis of body composition: revision of some quantitative assumptions. Annals of the New York Academy of Sciences, 110, 113-140.
Requires proper caliper technique. In untrained hands, error increases substantially; DEXA remains the reference method when accuracy matters.
Frequently asked questions
Which sites are measured?
Men: chest, abdomen and thigh. Women: triceps, suprailiac and thigh. Each skinfold is measured in millimeters with calipers, then summed and entered into the sex-specific Jackson-Pollock body-density equation, converted to body fat with the Siri equation.
How accurate is the skinfold method?
In trained hands, the 3-site Jackson-Pollock method correlates closely with DEXA and hydrostatic weighing. Error grows with poor technique, inconsistent site location and extreme body-fat levels, so use the same measurer and protocol for tracking.