What this calculator does
Skinfold callipers estimate body fat by pinching a fold of skin and subcutaneous fat at specific sites and measuring its thickness in millimetres. The Jackson-Pollock 3-site method, one of the most widely used skinfold protocols, combines three of those measurements with age and sex to estimate body density, which is then converted to a body fat percentage using the Siri equation.
The three sites differ by sex: chest, abdomen and thigh for men; triceps, suprailiac and thigh for women. This is a different technique to a tape-measure method such as the US Navy circumference formula: skinfolds measure subcutaneous fat thickness directly, rather than inferring body composition from body shape.
The formula
The three skinfold readings are summed, and that sum (plus age) is fed into a sex-specific regression equation to estimate body density in grams per millilitre. The Siri equation then converts that density into a body fat percentage: 495 divided by body density, minus 450.
| Term | Meaning |
|---|---|
| Skinfold | A pinched fold of skin and underlying fat, measured in millimetres with a calibrated calliper at a specific body site. |
| Body density | An estimate of the body's overall density, since fat tissue is less dense than lean tissue: a lower density implies a higher body fat percentage. |
| Siri equation | The standard formula converting an estimated body density into a body fat percentage: 495 / density − 450. |
The inputs explained
| Field | What to enter |
|---|---|
| Sex | Sex determines both the regression formula used and which three sites are measured. |
| Age (years) | Age in years, which is one of the terms in the density regression equation. |
| Skinfold 1 (chest / triceps) (mm) | Chest skinfold for men, or triceps skinfold for women. |
| Skinfold 2 (abdomen / suprailiac) (mm) | Abdomen skinfold for men, or suprailiac (hip bone) skinfold for women. |
| Skinfold 3 (thigh) (mm) | Thigh skinfold for both sexes. |
When to use it
Tracking body composition over time
Taken consistently by the same person at the same sites, skinfold measurements can track changes in body fat over weeks or months more sensitively than scale weight alone.
Comparing against a circumference-based estimate
Skinfold and circumference methods (such as the US Navy method) use entirely different inputs and can give somewhat different readings for the same person; neither is a substitute for a clinical measurement like DEXA.
Working with a coach or trainer
Because skinfold technique (calliper placement, pinch pressure, exact site location) strongly affects the result, this method is most reliable when a trained person takes the measurements the same way each time.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How estimated body fat changes as the chest skinfold increases
A 30-year-old man with a fixed 15 mm abdomen and 14 mm thigh skinfold, and the chest skinfold varied.
How estimated body fat changes with age at a fixed skinfold total
The same chest, abdomen and thigh readings (12, 15 and 14 mm), with age varied.
Questions
How accurate is the Jackson-Pollock 3-site method?
In the hands of a trained, consistent measurer it is a well-validated field method, typically within a few percentage points of laboratory methods such as hydrostatic weighing or DEXA. Self-measured skinfolds are far less reliable, since reaching the abdomen or thigh site accurately on yourself is difficult.
Why do the sites differ between men and women?
The regression equations were developed separately for each sex from population data, using the sites and combination found to correlate best with measured body density for that sex; the three sites are not interchangeable between the two equations.
Is this the same as the body fat calculator elsewhere on this site?
No. The body fat calculator uses the US Navy circumference method (waist, neck and, for women, hip measurements with a tape measure). This calculator uses skinfold callipers at different body sites entirely, a distinct measurement technique with its own formula.
Why does the result change with age at the same skinfold readings?
The regression equation includes age as a separate term because body fat distribution and the density of lean tissue both change with age, so two people with identical skinfold thickness but different ages are estimated to have somewhat different body fat percentages.
For a circumference-based estimate that needs only a tape measure, see the body fat percentage calculator.