What is the Skinfold Body Fat Test?
The skinfold body fat test is a widely used method for estimating body composition by measuring the thickness of subcutaneous fat (the fat beneath the skin) at specific body sites using a skinfold caliper. It is one of the most practical and cost-effective methods for assessing body fat percentage outside of a laboratory setting.
The test is based on the principle that subcutaneous fat is proportional to total body fat. By measuring skinfold thickness at multiple sites and applying validated regression equations, an estimate of overall body density and body fat percentage can be derived. The Durnin-Womersley method, developed in 1974, is one of the most commonly used 4-site protocols and is applicable to both men and women across a wide age range.
Skinfold measurements are used extensively in sports science, clinical nutrition, military fitness assessments, and public health research. When performed by a trained technician, skinfold measurements have an error margin of approximately 3–5% body fat compared to gold-standard methods like DEXA scanning.
Durnin-Womersley Formula
The Durnin-Womersley method first calculates body density from the logarithm (base 10) of the sum of four skinfold measurements, using age- and sex-specific coefficients:
The coefficients C (intercept) and M (slope) vary by age and sex:
| Age Range | Male C | Male M | Female C | Female M |
|---|---|---|---|---|
| 17–19 | 1.1620 | 0.0630 | 1.1549 | 0.0678 |
| 20–29 | 1.1631 | 0.0632 | 1.1599 | 0.0717 |
| 30–39 | 1.1422 | 0.0544 | 1.1423 | 0.0632 |
| 40–49 | 1.1620 | 0.0700 | 1.1333 | 0.0612 |
| 50+ | 1.1715 | 0.0779 | 1.1339 | 0.0645 |
Once body density is known, body fat percentage is calculated using the Siri equation:
Body Fat Categories
| Category | Men | Women |
|---|---|---|
| Essential Fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Measurement Technique
Accurate skinfold measurements require proper technique. Follow these guidelines for the best results:
- Use quality calipers: Harpenden, Lange, or Slim Guide calipers are recommended. Inexpensive plastic calipers may give less consistent readings.
- Measure on the right side: By convention, all measurements should be taken on the right side of the body.
- Pinch and pull: Grasp the skinfold firmly between your thumb and index finger, pulling it away from the underlying muscle. The fold should include two layers of skin and the subcutaneous fat.
- Place the caliper: Apply the caliper jaws approximately 1 cm below and at right angles to the pinch. Release the caliper handle fully and read within 2–3 seconds.
- Take multiple readings: Measure each site at least twice (ideally three times) and use the average. If readings differ by more than 2 mm, take additional measurements.
- Consistent conditions: Measure before exercise (not when the skin is moist) and at the same time of day for tracking purposes.
The Four Measurement Sites
Tricep
Measured on the back of the upper arm, halfway between the acromion (shoulder) and olecranon (elbow) processes. The arm should hang relaxed at the side. This is the most commonly measured site and reflects arm fat stores.
Bicep
Measured on the front of the upper arm, at the same level as the tricep measurement. The arm hangs relaxed, palm facing forward. This site complements the tricep measurement for a full picture of upper arm adiposity.
Subscapular
Measured just below the inferior angle of the scapula (shoulder blade). The fold runs diagonally, about 45 degrees to the horizontal. This site reflects trunk fat distribution.
Suprailiac
Measured just above the iliac crest (hip bone), in the mid-axillary line. The fold runs diagonally along the natural cleavage lines of the skin. This site is important for assessing abdominal adiposity.
Body Composition Methods Comparison
| Method | Accuracy | Cost | Accessibility | Notes |
|---|---|---|---|---|
| DEXA Scan | ±1–2% | High ($100–300) | Clinical only | Gold standard; measures bone, fat, lean |
| Hydrostatic Weighing | ±1.5–2.5% | Moderate | Lab only | Underwater weighing; uncomfortable for some |
| Bod Pod (ADP) | ±2–3% | Moderate | Lab/clinical | Air displacement plethysmography |
| Skinfold Calipers | ±3–5% | Low ($10–30) | Anywhere | Technician-dependent; portable |
| BIA (Bioelectrical) | ±3–8% | Low–Moderate | Home/gym | Affected by hydration status |
| Navy Tape Method | ±3–5% | Free | Anywhere | Uses circumference measurements only |
Worked Example
A 30-year-old male with the following skinfold measurements: Tricep = 12 mm, Bicep = 8 mm, Subscapular = 14 mm, Suprailiac = 16 mm.
log10(50) = 1.6990
D = 1.1422 − 0.0544 × 1.6990 = 1.0498
BF% = (495 ÷ 1.0498) − 450 = 21.5%
This falls within the Average body fat range for males (18–24%). The subject has a healthy amount of body fat, though could improve fitness by reducing toward the Fitness range (14–17%).
Frequently Asked Questions
How accurate are skinfold calipers?
When used by a trained practitioner, skinfold calipers have an error margin of approximately 3–5% compared to DEXA scanning. The key to accuracy is consistent technique and using the same technician for repeat measurements. Intra-individual tracking over time tends to be more reliable than single absolute measurements.
Which calipers should I use?
For clinical or research use, Harpenden calipers are considered the gold standard. For general fitness use, Slim Guide or Accu-Measure calipers offer good accuracy at a lower price. Avoid very cheap plastic calipers as they may lack the proper spring tension needed for consistent readings.
Can I measure my own skinfolds?
You can reliably self-measure the tricep, bicep, and suprailiac sites with practice. The subscapular site is difficult to reach on yourself. Having a partner take the measurements improves accuracy significantly. Consistency is more important than perfect technique for tracking changes over time.
How often should I measure?
For tracking body composition changes, measuring every 4–6 weeks is sufficient. Body fat changes slowly, and more frequent measurements may show more noise than signal. Always measure under the same conditions: same time of day, same side of body, before exercise, and when skin is dry.
Why does the formula use logarithms?
The relationship between skinfold thickness and body density is not linear — it follows a logarithmic curve. Using the log of the sum of skinfolds provides a better fit to the actual data across a wide range of body fat levels, particularly at higher skinfold values where the relationship would otherwise be underestimated.