Skinfold Body Fat Calculator (3-Site) Formula
Understand the math behind the skinfold body fat calculator (3-site). Each variable explained with a worked example.
Formulas Used
Body Fat Percentage
body_fat_pct = (495 / body_density) - 450Sum of Skinfolds
sum_of_skinfolds = sum3Body Density
body_dens = body_densityVariables
| Variable | Description | Default |
|---|---|---|
chest_mm | Chest Skinfold(mm) | 12 |
abdomen_mm | Abdomen Skinfold(mm) | 20 |
thigh_mm | Thigh Skinfold(mm) | 15 |
age | Age(years) | 30 |
sum3 | Derived value= chest_mm + abdomen_mm + thigh_mm | calculated |
body_density | Derived value= 1.10938 - 0.0008267 * sum3 + 0.0000016 * sum3 * sum3 - 0.0002574 * age | calculated |
How It Works
Jackson-Pollock 3-Site Method (Male)
Step 1: Body Density
D = 1.10938 - 0.0008267 x S + 0.0000016 x S^2 - 0.0002574 x Age
Where S = sum of chest + abdomen + thigh skinfolds in mm.
Step 2: Siri Equation
Body Fat % = (495 / D) - 450
This converts body density to body fat percentage.
Worked Example
A 30-year-old male with chest 12mm, abdomen 20mm, thigh 15mm.
chest_mm = 12abdomen_mm = 20thigh_mm = 15age = 30
- 01Sum = 12 + 20 + 15 = 47 mm
- 02D = 1.10938 - 0.0008267 x 47 + 0.0000016 x 2209 - 0.0002574 x 30
- 03= 1.10938 - 0.03885 + 0.00354 - 0.00772 = 1.06635
- 04Body Fat = (495 / 1.06635) - 450 = 14.1%
Ready to run the numbers?
Open Skinfold Body Fat Calculator (3-Site)