Body Fat Calculator: Jackson-Pollock 3-Site Calipers

 

Estimate adult body fat from three skinfold measurements using Jackson-Pollock body-density equations and the Siri conversion. This requires the correct caliper protocol; it is not a calculator from weight alone and does not directly measure body composition.

Published equation groupMen: chest, abdomen, thighWomen: triceps, suprailiac, thighAge (years)Chest skinfold (mm)Abdomen skinfold (mm)Thigh skinfold (mm)

Equation age scope: 18-61 years.

All folds use millimeters measured with skinfold calipers, not tape circumferences or centimeters. Changing equation group clears the fold entries because the required sites change.

JavaScript is required for interactive estimates. Formulas and method limitations remain available below.

Use the correct three-site protocol

The men's equation uses chest, abdomen and thigh skinfolds. The women's equation uses triceps, suprailiac and thigh skinfolds. These are distinct sets of measurement sites, not interchangeable labels for any three folds.

Obtain measurements using the relevant standardized Jackson-Pollock skinfold procedure, ideally with a trained assessor. Site location, fold direction, caliper placement and repeated measurement technique affect results. Do not substitute tape measurements, guessed thicknesses or folds taken using a different protocol.

How the body-density equations work

Let S be the sum of the three folds in millimeters and A age in years. The men's three-site equation is density = 1.10938 - 0.0008267 x S + 0.0000016 x S squared - 0.0002574 x A.

The women's three-site equation is density = 1.0994921 - 0.0009929 x S + 0.0000023 x S squared - 0.0001392 x A. Density is expressed in grams per cubic centimeter. These are regression estimates from published study groups, not universal laws.

Convert density to estimated body fat

The Siri two-component conversion is body fat (%) = 495 / density - 450. It assumes properties of fat and fat-free tissue that may not apply equally to every person or population. The calculator does not claim applicability to every athlete, ancestry group or clinical situation.

The original equation groups are labeled men and women to reflect the published models. Choosing a group does not establish that the original calibration is appropriate for you. The tool does not assess how medical conditions, hormone treatment, pregnancy or other changes may affect applicability.

Worked example

Choose Published equation group Men: chest, abdomen, thigh. Enter Age (years) 30, Chest skinfold (mm) 12, Abdomen skinfold (mm) 20 and Thigh skinfold (mm) 16. Select Estimate body fat.

The sum S is 48 mm. The density equation gives 1.0656628 g/cm3. The Siri conversion gives approximately 14.50% body fat. This example demonstrates the arithmetic and does not establish a healthy target or a clinical conclusion.

Age scope and input limits

This tool restricts the men's equation to ages 18-61 and the women's equation to ages 18-55, reflecting the age ranges of the original adult studies rather than extending the equations to children or older adults. Each entered fold must be 2-60 mm as a software guardrail.

Those thickness limits do not independently validate a measurement or guarantee that all accepted combinations match the original calibration population. If a fold cannot be reliably measured with the available caliper or method, do not invent a value to obtain a result.

Interpretation and alternatives

Measurement error can meaningfully change the estimate. Displayed decimals are calculation detail, not evidence of individual accuracy. Repeating measurements consistently can support tracking, but small apparent changes may reflect technique rather than a true composition change.

No fitness categories, ideal percentage or weight-loss recommendations are assigned. The Adult BMI Calculator addresses a different height-and-weight measure; BMI does not directly measure body fat either.

Sources

Jackson and Pollock (1978), Generalized equations for predicting body density of men. Jackson, Pollock and Ward (1980), Generalized equations for predicting body density of women. Siri (1961), Body composition from fluid spaces and density: analysis of methods, in Techniques for Measuring Body Composition.

For a step-by-step walkthrough, read How to Calculate Body Fat with Jackson-Pollock 3-Site Skinfolds.

Privacy

Calculations run locally in your browser. This calculator does not save or transmit measurements. The hosting website may use separate analytics or advertising services.