How this calculator works
Table 5 of Durnin and Womersley supplies sex- and age-specific intercepts and slopes for the logarithm of four skinfolds. Siri converts estimated density to fat fraction. This page uses only age groups actually sampled in the original paper, rather than adding an unverified under-17 band. Trained caliper technique is essential; a tape circumference is not a skinfold thickness. The result is an estimate for information only and is not medical advice.
Formula
Density (g/cm³) = c - m log10(sum of four skinfolds in mm), using Table 5 coefficients. Body fat (%) = 495/density - 450.
Worked example
For a male aged 25 whose four sites total 100 mm, density = 1.1631 - 0.0632 x 2 = 1.0367 g/cm³; estimated body fat is about 27.48%.
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Frequently asked questions
Which four sites are required?
Biceps, triceps, subscapular and suprailiac skinfolds. Do not substitute waist or hip circumference.
Can I use this for a child?
No. Only the original sampled age ranges are supported here.
Why can the result differ from DXA?
Caliper technique and assumptions about fat-free tissue density introduce error. The result is an estimate from a particular population model.