SKINFOLD
BODY FAT
Estimate body fat using the Jackson-Pollock 3-site skinfold method.
The Jackson-Pollock Skinfold Method
The Jackson-Pollock 3-site skinfold method is a widely used, validated technique for estimating body fat percentage using skinfold calipers. For men, measurements are taken at the chest, abdomen, and thigh. For women, at the tricep, suprailiac (above the hip bone), and thigh. The sum of these three measurements, combined with age, is entered into the Siri body-density equation, which converts estimated body density into a body fat percentage.
How to Measure Skinfolds
Skinfold calipers pinch a fold of skin and the fat directly beneath it, away from the underlying muscle, and measure its thickness in millimeters. For consistent results, take each measurement on the right side of the body, pinch firmly about 1cm above the marked site, and read the caliper dial about two seconds after applying pressure. Take two or three readings per site and use the average — skin compresses slightly under the caliper, so a single reading can vary from the true value.
Common Measurement Mistakes
- Inconsistent site location: Even a small shift in where the fold is pinched can change the reading by several millimeters.
- Measuring over clothing: Always measure on bare skin.
- Releasing the caliper too quickly: Skin takes a moment to settle; reading too fast tends to overestimate thickness.
- Comparing results across different measurers: Technique varies between people, so track your own trend over time rather than comparing your numbers to someone else's.
Interpreting Your Result
The percentage this calculator returns is an estimate, not a diagnostic measurement. Use it primarily to track your own trend over weeks or months rather than to fixate on a single number. A falling sum of skinfolds over time is generally a more reliable signal of fat loss than any one body fat percentage reading, since it removes some of the error introduced by the density-conversion formula.
Accuracy and Limitations
When performed correctly by a trained measurer, the JP3 method has a standard error of approximately 3.5% compared to hydrostatic weighing, one of the reference methods used in body-composition research. Key sources of error include measurement technique, caliper quality, and biological variation such as skin compressibility and fat distribution patterns, which the Jackson-Pollock equations do not fully account for across every body type. Consistency in measurement site and technique matters more than the absolute precision of any single reading. This tool is intended for general fitness tracking and education; it does not replace clinical body-composition testing such as DEXA, hydrostatic weighing, or air displacement plethysmography, and it should not be used to self-diagnose a medical condition.