Clinical Medicine & Physiology
Slaughter Pediatric Skinfold Body Fat % Calculator: Triceps + Subscapular (Ages 8–18)
Estimate child and adolescent Percent Body Fat (%BF) from Triceps + Subscapular skinfolds S_2 (mm) using Mary H. Slaughter et al.’s (1988, Human Biology) multicomponent-validated quadratic (S_2 <= 35 mm) and linear (S_2 > 35 mm) youth equations.
Why adult Siri densitometry overestimates pediatric body fat — and how Slaughter (1988) solved it!
Children have higher water content and lower bone mineral content inside their fat-free mass than adults (FFM density ~1.084 g/cm^3 in pre-pubertal children vs 1.100 g/cm^3 in adults), causing adult Siri equations to overestimate child body fat by 3%–6%! Calibrating against 4-compartment body water + bone mineral + hydrostatic density across 310 children and youths aged 8 to 18 years, Mary H. Slaughter et al. (1988, Human Biology; FitnessGram standard) published exact two-site equations using S_2 = Triceps + Subscapular (mm):
When S_2 <= 35 mm: Pubescent Boys use %BF = 1.21 * S_2 - 0.008 * (S_2^2) - 3.4 (Pre-pubescent -1.7, Post-pubescent -5.5), and Girls (all maturation stages) use %BF = 1.33 * S_2 - 0.013 * (S_2^2) - 2.5! When S_2 > 35 mm (where quadratic terms would bend downward), Slaughter switches cleanly to linear equations: Boys %BF = 0.783 * S_2 + 1.6 and Girls %BF = 0.546 * S_2 + 9.7!
| Youth Cohort & Skinfold Sum S_2 = Triceps + Subscapular | Slaughter (1988) Regime | Evaluated Body Fat (%) |
|---|---|---|
| Pubescent Boy (Triceps 10 + Subscap 8 = 18 mm) | Quadratic <= 35 mm (-3.4 intercept) | 15.79% BF |
| Girl (Triceps 12 + Subscap 10 = 22 mm) | Quadratic <= 35 mm (-2.5 intercept) | 20.47% BF |
| Boy with Elevated Folds (24 + 20 = 44 mm > 35) | Linear > 35 mm (0.783 * S_2 + 1.6) | 36.05% BF |
| Girl with Elevated Folds (24 + 20 = 44 mm > 35) | Linear > 35 mm (0.546 * S_2 + 9.7) | 33.72% BF |
Slaughter (1988) Pediatric Triceps + Subscapular %BF (Quadratic <= 35 mm / Linear > 35 mm)
Evaluates pubescent Boys ("M") or Girls ("F") Slaughter %BF across Triceps B2 (mm), Subscapular B3 (mm), and Sex B4 ("M" or "F"), switching automatically at S_2 = 35 mm.
=IF(OR(B2 <= 1, B3 <= 1, B2 + B3 > 130, AND(B4 <> "M", B4 <> "F")), "Invalid Triceps/Subscapular Skinfolds (mm) or Sex (M/F)", ROUND(IF(B4 = "M", IF(B2 + B3 <= 35, 1.21 * (B2 + B3) - 0.008 * ((B2 + B3) ^ 2) - 3.4, 0.783 * (B2 + B3) + 1.6), IF(B2 + B3 <= 35, 1.33 * (B2 + B3) - 0.013 * ((B2 + B3) ^ 2) - 2.5, 0.546 * (B2 + B3) + 9.7)), 2))Two-Site Pediatric Skinfold Sum S_2 (mm) & Regime Indicator
Reports whether S_2 = B2 + B3 uses Slaughter’s <= 35 mm quadratic curve or > 35 mm high-fold linear curve.
=IF(OR(B2 <= 1, B3 <= 1, B2 + B3 > 130), "Invalid Skinfolds", IF(B2 + B3 <= 35, "S_2 <= 35 mm: Slaughter Quadratic Regime", "S_2 > 35 mm: Slaughter Linear High-Fold Regime"))Try the example
Use the original values or change them to test your understanding.