AkCalculators

Skinfold testing explained — how it estimates body fat and how to improve accuracy

Skinfold measurement with calipers is a classic, inexpensive method for estimating body composition. By sampling the thickness of subcutaneous fat at standardized sites across the body, skinfold equations approximate body density; body density is then converted into percentage body fat using formulas such as the Siri equation. When performed correctly by a trained assessor, skinfold testing provides a reliable way to track changes in body composition over time.

How the calculation works

This calculator implements the Jackson & Pollock 3-site and 7-site equations. The general steps are: (1) measure skinfold thicknesses at the specified sites (in mm), (2) sum the skinfolds or use the appropriate sum in the sex-specific regression formula to estimate body density, and (3) convert body density to body fat percentage using the Siri equation:

% body fat = (495 / body density) − 450

Which sites to use — 3-site vs 7-site

The 3-site protocol is quick and commonly used in field settings: for men it uses chest, abdomen and thigh; for women it uses triceps, suprailiac and thigh. The 7-site method samples chest, midaxillary, triceps, subscapular, abdomen, suprailiac and thigh — it can reduce sampling bias by measuring more regions but takes longer.

Sources of error and how to reduce them

Accuracy depends more on measurement technique than the equation chosen. Common sources of error:

• Poor site identification: Learn anatomical landmarks and be consistent.
• Wrong pinch technique: Pull a firm double-thickness of skin and fat (not muscle) before applying the caliper.
• Caliper quality: Use a calibrated, good-quality caliper and read at the correct time after applying pressure (usually 1–2 seconds).
• Inter-tester variability: Have the same trained person measure you each time for best consistency.
• Hydration & recent exercise: Measure under similar conditions (same time of day, similar hydration) to improve repeatability.

Interpreting results

Skinfold-derived body fat percentage gives an estimate — fitness practitioners often accept ±3–4% error when testing is done well. Use these estimates for tracking trends (loss or gain of fat) rather than as a precise clinical measurement. For clinical precision you might consider DEXA or hydrostatic weighing.

Practical tips for accurate testing

• Practice site location and measurement technique with a trained partner or coach.
• Take each skinfold measurement 2–3 times and use the average.
• Record time of day, hydration status, and recent exercise — repeat under similar conditions.
• When tracking change, always use the same method (3-site or 7-site) and the same assessor if possible.

Using this calculator

Select male or female, choose 3-site or 7-site, enter measured skinfolds in millimetres, and provide age and body weight. The tool computes body density via the Jackson & Pollock equations and then converts to percentage body fat (Siri). It also returns fat mass and lean mass in kg and lb when you supply bodyweight and units.

Disclaimer: This calculator estimates body fat using population-based equations. It is intended for fitness and educational use, not for diagnosis. For medical or athletic performance decisions consult a qualified professional.