Guedes 3-Site Skinfold Calculator: Body Fat Percentage

By PounceFit Team · Updated on 2026-10-06

Technical content for health and fitness professionals. It reproduces formulas and protocols published in the scientific literature, with the sources at the end of the page. It is not a recommendation and does not replace the judgment of the professional who runs the assessment.

Free Guedes (1985) 3-site skinfold calculator, a Brazilian protocol: body fat percentage with the same math as PounceFit, the body assessment app.

The Guedes 3-site skinfold calculator estimates body fat percentage from three skinfolds, with equations developed with Brazilian university students (Guedes, 1985). The equation calculates body density from the logarithm of the skinfold sum, and the Siri equation converts density to body fat (Siri, 1961). The math is the same as in PounceFit, body assessment software.

Who it is for

Young adults with a profile close to the original sample of Brazilian university students (Guedes, 1985). The sites differ by sex:

• Men: triceps, suprailiac and abdominal.
• Women: thigh, suprailiac and subscapular.

The original sample comprised 206 university students, most of them physical education students at the Federal University of Santa Maria, in southern Brazil: 110 men aged 17 to 27 and 96 women aged 17 to 29. Body density was measured by hydrostatic weighing (Cursino, 2009).

Formula

S = sum of the three skinfolds, in mm. log is the base-10 logarithm.

• Men: density = 1.17136 − 0.06706 × log(S)
• Women: density = 1.1665 − 0.07063 × log(S)
• Body fat (%) = (4.95 ÷ density − 4.50) × 100

The equation does not use age.

Worked example

Man, 22 years old, 75 kg (165 lb). Skinfolds (mm): triceps 10, suprailiac 14, abdominal 18.

1. S = 42 mm; log(42) = 1.6232.
2. Density = 1.17136 − 0.06706 × 1.6232 = 1.0625049.
3. Body fat = (4.95 ÷ 1.0625049 − 4.50) × 100 = 15.9%.
4. Fat mass = 11.9 kg; fat-free mass = 63.1 kg.

Limitations

• It was developed with a specific group of university students. In older clients or very different profiles, accuracy may be lower, as with skinfold equations in general (Heyward and Wagner, 2004).
• Age is not part of the equation, so the same skinfold sum gives the same result at any age.
• The result is an estimate (Heyward and Wagner, 2004). Use the standardized measurement sites (ACSM, 2021) and keep the same protocol at every reassessment.