Skinfold Body Fat Calculator (Jackson–Pollock 3-Site, Siri Equation)
Body fat percentage, body density and fat and lean mass from three skinfold caliper readings, by the Jackson–Pollock 3-site method.
Results
What this tool does
Jackson and Pollock published their regression equations in 1978: three skinfolds give the body density, and Siri's 1961 equation turns density into a percentage of fat. Men use chest, abdomen and thigh; women use triceps, suprailiac and thigh. Take every reading on the right side of the body, pinch the skin and fat but not the muscle, read after a couple of seconds, repeat each site at least twice and use the average. Even done well the method is typically a few percentage points away from a DEXA scan, so it is best for following your own changes with the same person and caliper.
Formula
density: men 1.10938 − 0.0008267 Σ + 0.0000016 Σ² − 0.0002574 age · women 1.0994921 − 0.0009929 Σ + 0.0000023 Σ² − 0.0001392 age · body fat % = 495 ÷ density − 450 (Siri)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
sx | Sex | — |
ag | Age | a |
s1 | Skinfold 1: chest (men) or triceps (women) | mm |
s2 | Skinfold 2: abdomen (men) or suprailiac (women) | mm |
s3 | Skinfold 3: thigh (both sexes) | mm |
kg | Body weight | kg |
BF | Body fat | % |
BD | Body density | g/cm³ |
SM | Sum of the three skinfolds | mm |
FM | Fat mass | kg |
LM | Lean body mass | kg |
Worked example
- Sex1
- Age30 a
- Skinfold 1: chest (men) or triceps (women)12 mm
- Skinfold 2: abdomen (men) or suprailiac (women)20 mm
- Skinfold 3: thigh (both sexes)15 mm
- Body weight78 kg
- Body fat14.2 %
- Body density1.0663 g/cm³
- Sum of the three skinfolds47 mm
- Fat mass11.1 kg
- Lean body mass66.9 kg
Limitations
- This tool is informational only. It does not diagnose, treat or replace a qualified health professional. Speak to a doctor before making decisions about your health.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.