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Cartwright Professional Assessment Tool

3-Site Skinfold Body Fat Calculator

Estimate body density and body-fat percentage from three skinfold measurements using the Jackson–Pollock equations and Siri body-density conversion.

The original male and female equations use different skinfold sites.
Select sex to see the validated age range.
Enter the skinfold thickness in millimetres.
Enter the skinfold thickness in millimetres.
Enter the skinfold thickness in millimetres.
Body-fat percentage is estimated from body density using the Siri equation.
Measurement sites: select sex to display the three sites required by the original equation.
Evidence-based Jackson–Pollock equations Hydrostatic-validation studies Siri body-density conversion
Estimated body fat
—
%
Result type Estimated body-fat percentage Enter three correctly measured skinfolds to calculate a result.
Skinfold sum —
Estimated body density —
Equation —
Age —

Measurement sites

Jackson–Pollock 3-site equations use different anatomical sites for males and females.

Site 1 —
Site 2 —
Site 3 —
Body density equation Select sex to display the appropriate equation.
Body-fat conversion Siri: Body Fat % = (495 ÷ Body Density) − 450

How to perform a 3-site skinfold assessment

Measurement protocol

  1. Identify and mark the correct anatomical skinfold site.
  2. Measure directly on skin rather than through clothing.
  3. Grasp a double fold of skin and subcutaneous tissue firmly between thumb and forefinger.
  4. Place the caliper jaws approximately 1 cm from the fingers while continuing to hold the skinfold.
  5. Allow the caliper to apply its measuring pressure and take the reading consistently.
  6. Record the thickness in millimetres.
  7. Repeat measurements rather than relying on a single pinch.
  8. Use the same assessor, caliper and protocol for repeat testing whenever possible.

Need professional skinfold measurement equipment?

Skinfold assessment depends heavily on consistent site location, measurement technique and caliper pressure. Professional equipment helps improve repeatability in fitness, sports science and health assessment.

Explore Skinfold Calipers Read the 3-Site Guide

Jackson–Pollock 3-site measurement sites

Male equation

  • Chest: diagonal skinfold on the chest.
  • Abdomen: vertical abdominal skinfold.
  • Thigh: vertical skinfold on the anterior thigh.

The generalized male equation was developed using adult men aged 18–61 years.

Female equation

  • Triceps: vertical skinfold on the posterior upper arm.
  • Suprailiac: diagonal skinfold above the iliac crest.
  • Thigh: vertical skinfold on the anterior thigh.

The generalized female equation was developed in women aged 18–55 years. The original authors advised caution when applying the equation to women over 40.

Understanding your result

Skinfold calipers do not directly measure whole-body fat percentage. They measure the thickness of selected subcutaneous skinfolds. The Jackson–Pollock equation uses those measurements plus age to estimate body density.

The Siri equation then converts estimated body density into an estimated body-fat percentage. Consequently, the percentage produced here should not be interpreted as a direct measurement equivalent to chemical analysis or a multi-compartment laboratory method.

Best use: skinfold assessment is particularly useful for repeat monitoring when measurements are performed by a skilled assessor using the same sites, equipment and technique. Changes in the raw sum of skinfolds can be valuable even when the absolute estimated body-fat percentage has uncertainty.

Limitations of skinfold body-fat estimation

The Jackson–Pollock equations were derived from specific research populations and estimate body density statistically. Measurement error can also arise from incorrect anatomical landmarks, inconsistent folds, assessor technique and caliper differences.

The Siri conversion is a two-compartment model and assumes characteristic densities for fat and fat-free tissue. Those assumptions are not identical in every individual or population.

For these reasons, body-fat percentage from skinfolds is best reported as an estimate, while repeatable skinfold thickness and the summed skinfold measurement provide useful longitudinal information.

Frequently asked questions

What is the Jackson–Pollock 3-site body fat test?
It is a skinfold assessment method that uses three anatomical skinfold measurements and age to estimate body density. The male and female equations use different measurement sites.
Which three skinfold sites are used for men?
The Jackson–Pollock male 3-site equation uses chest, abdomen and thigh skinfold measurements.
Which three skinfold sites are used for women?
The Jackson, Pollock and Ward female 3-site equation uses triceps, suprailiac and thigh skinfold measurements.
Does the calculator directly measure body fat?
No. The calipers measure subcutaneous skinfold thickness. Those measurements are used to estimate body density, which is then converted to estimated body-fat percentage.
Why does age affect the calculation?
Age is included as a term in the original Jackson–Pollock generalized equations because the relationship between skinfolds and body density changes with age.
How many times should each skinfold be measured?
Repeat measurements are preferable to relying on a single pinch. If readings differ meaningfully, repeat the site and use a standardised measurement protocol. Consistency is particularly important when monitoring changes over time.
Why might my skinfold result differ from a body-composition scale?
The methods estimate body composition differently. Skinfolds use measured subcutaneous tissue and prediction equations, while most body-composition scales use bioelectrical impedance. The results are therefore not expected to be identical.
Can I use this calculator outside the published age range?
No. This calculator deliberately restricts inputs to the age ranges of the original generalized-equation studies rather than extrapolating the equations into unvalidated ages.

Scientific methodology & references

Male equation:
Jackson AS, Pollock ML. Generalized equations for predicting body density of men. British Journal of Nutrition. 1978;40(3):497–504. DOI: 10.1079/BJN19780152.

The study measured skinfolds and laboratory body density in adult men. The generalized equations were developed in 308 men and cross-validated in a separate sample of 95 men aged 18–61 years.

Female equation:
Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Medicine & Science in Sports & Exercise. 1980;12(3):175–181.

The female study developed generalized body-composition equations from 249 women aged 18–55 years and cross-validated them in a separate sample of 82 women. The authors specifically advised caution when applying the equations to women over age 40.

Body-fat conversion:
Siri WE. Body composition from fluid spaces and density: analysis of methods. In: Techniques for Measuring Body Composition. National Academy of Sciences; 1961:223–244.

Calculation:
Male body density = 1.10938 − 0.0008267(S) + 0.0000016(S²) − 0.0002574(age). S is chest + abdomen + thigh skinfolds in millimetres.

Female body density = 1.0994921 − 0.0009929(S) + 0.0000023(S²) − 0.0001392(age). S is triceps + suprailiac + thigh skinfolds in millimetres.

Estimated body-fat percentage = (495 ÷ estimated body density) − 450.

  • Methodology reviewed: September 2026
  • Calculator version: 1.0
  • Purpose: Professional education and benchmarking
  • Male equation population: adult men aged 18–61
  • Female equation population: adult women aged 18–55
  • Output: estimated body density and estimated body-fat percentage

This calculator is not a diagnostic tool. Body-fat percentage is an estimate derived from anthropometric measurements and prediction equations. Measurement technique and population differences can materially affect results.

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