What Is Skinfold Thickness?
Skinfold thickness is a direct measurement of subcutaneous fat at specific body sites using a caliper. It is one of the most accessible and widely used methods for estimating body fat percentage. By measuring the double layer of skin and underlying fat, trained testers can predict total body fat with high accuracy. The Jackson‑Pollock 3‑site skinfold method (using chest, abdomen, and thigh for men; triceps, suprailiac, and thigh for women) is a validated, popular protocol in fitness and clinical settings.
Jackson‑Pollock 3‑Site Formula
This calculator implements the generalized equations developed by Jackson & Pollock (1978, 1980). They convert the sum of three skinfolds into body density, then into body fat percentage using the Siri equation.
Body Density = 1.10938 – 0.0008267 × Σ + 0.0000016 × Σ² – 0.0002574 × Age
For Women (triceps, suprailiac, thigh):
Body Density = 1.0994921 – 0.0009929 × Σ + 0.0000023 × Σ² – 0.0001392 × Age
Where Σ = sum of three skinfolds (mm).
Body Fat % = (495 / Body Density) – 450
Note: The calculator uses the chest, abdomen, and thigh for men and triceps, suprailiac, and thigh for women. If you measured other sites, please use a different protocol.
How to Measure Skinfolds (Step‑by‑Step)
- Equipment: Use a high‑quality skinfold caliper (e.g., Harpenden, Lange, or Slim Guide).
- Identify sites:
- Chest (men only): Diagonal fold midway between the axilla and nipple.
- Abdomen (men only): Vertical fold 2‑3 cm to the right of the umbilicus.
- Thigh: Vertical fold on the anterior midline of the thigh, midway between hip and knee.
- Triceps (women only): Vertical fold on the posterior midline of the upper arm, midway between shoulder and elbow.
- Suprailiac (women only): Diagonal fold just above the iliac crest (hip bone) at the midaxillary line.
- Technique: Pinch the skinfold firmly with thumb and forefinger, place the caliper jaws perpendicular to the fold, and read to the nearest 0.5 mm after 2 seconds.
- Repeat: Take at least two measurements at each site; if they differ by more than 1 mm, take a third and average.
- Enter the average values into the calculator (in mm).
Example Calculation
Subject: 35‑year‑old male, chest 12 mm, abdomen 18 mm, thigh 22 mm.
- Sum Σ = 12 + 18 + 22 = 52 mm
- Body Density = 1.10938 – 0.0008267×52 + 0.0000016×52² – 0.0002574×35 = 1.0725
- Body Fat % = (495 / 1.0725) – 450 = 11.6%
This result would be considered in the “Athletic” or “Fitness” category for a man of that age.
Body Fat Percentage Categories
Use the table below to interpret your results (adapted from the American Council on Exercise).
| Category | Men (% fat) | Women (% fat) |
|---|---|---|
| Essential Fat | 2–5% | 10–13% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Frequently Asked Questions About Skinfold Testing
How accurate is the skinfold method?
When performed by a trained technician using quality calipers, the skinfold method has a prediction error of about 3‑5% body fat compared to reference methods (e.g., DEXA). Consistency is key – always measure at the same sites, on the same side of the body, and under similar conditions.
Can I use this calculator if I’m very lean or very obese?
The Jackson‑Pollock equations are most accurate for adults with body fat within the typical range (about 8‑40% for men, 15‑45% for women). For extremely lean or obese individuals, the error may be larger. In those cases, methods like bioelectrical impedance or DEXA may be more appropriate.
What if I don’t have a skinfold caliper?
Skinfold calipers are affordable (starting at $10‑$20) and widely available online. Alternatively, you can have measurements taken by a fitness professional at a gym or health clinic. This calculator is designed for those who have access to calipers.
Why does the formula differ for men and women?
Men and women store fat differently due to hormonal and physiological differences. Men tend to accumulate more fat in the trunk (android pattern), while women store more in the hips and thighs (gynoid pattern). The Jackson‑Pollock equations use gender‑specific sites and coefficients to account for these patterns, improving accuracy.
How often should I measure skinfolds?
For tracking changes, measure every 4‑6 weeks. Fat loss (or gain) occurs slowly, and more frequent measurements can be misleading due to normal fluctuations in hydration and measurement error. Always measure at the same time of day (preferably morning) and before exercise.
Tips for Accurate Skinfold Measurement
- Always measure on the right side of the body (standard protocol).
- Pinch the skinfold firmly – don’t include muscle.
- Read the caliper dial 2 seconds after releasing the trigger.
- Repeat measurements until consistent, then average.
- Avoid measuring immediately after exercise (fluid shifts may alter readings).
- Use the same caliper each time for consistency.