Understanding the Durnin-Womersley Skinfold Method

The Durnin-Womersley method is a widely used technique to estimate body fat percentage based on the measurement of skinfold thickness at four specific sites: biceps, triceps, subscapular, and suprailiac. These measurements are then used in a series of equations to calculate body density, which is subsequently converted into body fat percentage.

How the Calculation Works

The core principle behind skinfold measurements is that a significant portion of the body's fat is stored directly under the skin (subcutaneous fat). By measuring the thickness of these skinfolds, we can estimate total body fat. The Durnin-Womersley method involves two main steps:

1. Calculate Body Density: The sum of the four skinfold measurements is used in age and gender-specific regression equations to predict body density (g/ml).
2. Convert Density to Body Fat Percentage: The calculated body density is then converted into a body fat percentage using a standard formula, most commonly the Siri or Brozek equation.

Formulas Used

First, calculate the sum of the four skinfolds (biceps, triceps, subscapular, suprailiac) in millimeters.

Then, use the appropriate body density formula based on age and gender. Here are examples for a specific age range (e.g., 20-29 years):

For Men (20-29 years):
Body Density = 1.1631 - (0.0632 * log10(Sum of 4 Skinfolds))

For Women (20-29 years):
Body Density = 1.1599 - (0.0717 * log10(Sum of 4 Skinfolds))

Note: Coefficients vary for different age groups.

Finally, convert body density to body fat percentage using the Siri equation:

Body Fat Percentage (%) = (495 / Body Density) - 450

Step-by-Step Example

Let's calculate the body fat percentage for a 25-year-old male with the following skinfold measurements:

• Biceps: 8 mm
• Triceps: 12 mm
• Subscapular: 15 mm
• Suprailiac: 10 mm

1. Sum of 4 Skinfolds: 8 + 12 + 15 + 10 = 45 mm
2. Calculate Body Density (for 20-29 year old male):
   Body Density = 1.1631 - (0.0632 * log10(45))
log10(45) ≈ 1.6532
Body Density = 1.1631 - (0.0632 * 1.6532)
Body Density = 1.1631 - 0.1045
Body Density ≈ 1.0586 g/ml
3. Calculate Body Fat Percentage:
   Body Fat Percentage = (495 / 1.0586) - 450
Body Fat Percentage = 467.60 - 450
Body Fat Percentage ≈ 17.6%

Based on this example, the estimated body fat percentage for this individual is approximately 17.6%.

Body Fat Percentage Categories

Here are general guidelines for body fat percentage categories for men and women: