Slaughter Skinfold Body Fat Calculator (Children)

How it is calculated

The tool adds the two skinfold readings in millimetres, S = triceps + calf, and converts the sum to a body-fat percentage with a sex-specific line. For boys: %fat = 0.735 × S + 1.0 when S is 35 mm or less, and %fat = 0.783 × S + 1.6 when S is above 35 mm. For girls: %fat = 0.610 × S + 5.1, with no split. The category then compares the result with fixed cut-offs: for boys below 10 is Low, 10 to 20 Optimal, 20 to 25 Moderately high and 25 or more High; for girls below 15, 15 to 25, 25 to 30 and 30 or more. Each skinfold must be above 0 and at most 100 mm, otherwise there is no result. Sex is male or female; if left empty it is taken as male, and any other value gives no result. Age is not an input and does not change the result.

Common mistakes

• Using the adult skinfold logic for a child: this tool is meant for children and teenagers, and an adult should use an adult equation.
• Entering centimetres instead of millimetres. A 14 mm fold typed as 1.4 gives a tiny, meaningless percentage.
• Taking the triceps and calf folds at the wrong sites, on the wrong side or with a caliper not held perpendicular to the fold. A 2 mm difference moves the result by more than a percentage point.
• Choosing the wrong sex, which changes both the equation and the category cut-offs, or leaving sex empty for a girl, which is read as male.
• Expecting age to refine the answer. The inputs are skinfolds and sex only, so the same readings give the same percentage at any age.