Durnin-Womersley Skinfold Calculator
Enter the four Durnin-Womersley skinfold measurements to estimate body density and body fat. The calculator also reverses the selected conversion equation to show the four-site sum corresponding to a target estimate.
Selected body-fat estimate (Siri)21.53%
- Four-site skinfold sum
- 50
- Estimated body density
- 1.05
- Siri body-fat estimate
- 21.53%
- Brožek body-fat estimate
- 21.13%
- Conversion-method spread
- 0.4%
- Estimated fat mass
- 16.15
- Estimated fat-free mass
- 58.85
- Target four-site skinfold sum
- 35.76
- Change from current skinfold sum
- 14.24
- Equation used
- Male, age 30-39: c = 1.1422, m = 0.0544
How to use this calculator
- Select the sex category and age band used by the original Durnin-Womersley equation.
- Enter your current weight if you want the accompanying fat-mass and fat-free-mass estimates.
- Enter biceps, triceps, subscapular, and suprailiac skinfolds in millimeters.
- Choose Siri or Brožek for the mass and target calculations, then enter the target body-fat estimate.
How the four-site estimate is calculated
The Durnin-Womersley method adds four caliper measurements: biceps, triceps, subscapular, and suprailiac. It uses the base-10 logarithm of that sum with an age- and sex-specific regression to estimate body density. The calculator selects the coefficient row for the entered age and the sex category used in the original study.
S = biceps + triceps + subscapular + suprailiac
body density = c − m × log10(S)
The density is shown with both commonly used conversions: Siri % fat = 495 ÷ density − 450 and Brožek % fat = 457 ÷ density − 414.2. The selected conversion controls the displayed fat mass, fat-free mass, and target calculation. Fat mass is body weight times the selected percentage, and fat-free mass is the remainder.
How the target skinfold sum works
The target is not a separate prediction model. The calculator first rearranges the chosen density conversion for the density implied by the target percentage, then rearranges the Durnin-Womersley equation:
target density = K ÷ (target % + C)
target sum = 10^((c − target density) ÷ m)
A positive change from the current sum means the target sum is lower. A negative change means the selected target percentage is higher than the current estimate. The result is a total across four sites, not an instruction to change any one site by a particular amount.
What moves the result most
The four measurements and their consistency matter most. A small change in one fold changes the sum and, through the logarithm, the estimated density. Age can change the estimate even when the measurements are identical because the original regression uses different coefficient bands. Siri and Brožek convert the same density differently, so the calculator shows their spread instead of treating either as a universal answer.
What the calculation leaves out
This is a two-compartment density estimate, not a direct measurement of fat tissue. It does not account for individual differences in bone mineral, hydration, visceral fat, body shape, training history, or the population limits of the original regressions. It also cannot correct for caliper pressure, site location, pinching technique, or transcription errors. Repeated measurements by a trained, consistent measurer are usually more useful for tracking than a single isolated reading.
Worked example
For a 30-year-old male who weighs 75 kg, suppose the biceps, triceps, subscapular, and suprailiac measurements are 5, 10, 15, and 20 mm. The four-site sum is 50 mm. The male 30-39 coefficients are c = 1.1422 and m = 0.0544, giving a body density of about 1.0498.
The Siri conversion gives about 21.5% body fat and the Brožek conversion about 21.1%. With Siri selected, the 75 kg estimate is about 16.1 kg fat mass and 58.9 kg fat-free mass. An 18% Siri target reverses to a four-site sum of about 35.8 mm, so the target is about 14.2 mm below the current total.
Common questions
Where are the four Durnin-Womersley skinfold sites?
The four sites are biceps on the front of the upper arm, triceps on the back of the upper arm, subscapular below the shoulder blade, and suprailiac above the iliac crest. The study method specifies site locations and fold directions, so use a standardized measurement protocol rather than approximate landmarks.
Why does age change the body-fat estimate?
The Durnin-Womersley equations use different regression coefficients for age bands. With the same skinfold sum, selecting a different age band can therefore give a different body-density estimate. This reflects the fitted study equations, not a direct observation that your body composition changed on your birthday.
What is the difference between the Siri and Brožek equations?
Both equations turn estimated body density into a body-fat percentage, but they use different constants. They will usually produce similar but not identical values from the same density. This calculator displays both and uses your selection only for the mass and reverse-target results.
Why should skinfold measurements be repeated?
Caliper placement, pinch technique, pressure, and reading the dial can all affect a measurement. Taking repeated readings at the same marked sites, ideally by the same trained measurer, reduces random variation. Compare like-for-like measurements when following a trend.
What does the target skinfold sum mean?
It is the total of the four measurements that would produce your chosen body-fat estimate under the selected equations. It does not predict where change will occur or how quickly it will happen. Individual skinfold sites do not necessarily change in equal proportions.
Can results from different skinfold methods be compared?
Not directly without care. Different site sets, calipers, equations, and conversion methods can give different estimates even from the same person. Keep the method, sites, and measurer consistent when comparing measurements over time.