Body Fat Calculator (3-Site Skinfold)

About the Body Fat Calculator (3-Site Skinfold)

The Jackson-Pollock 3-site skinfold test is a practical field method for estimating body fat percentage with a caliper. It uses three measurement sites to estimate body density and then converts that result into body fat percentage.

The measurement sites differ by sex. Men use chest, abdomen, and thigh. Women use triceps, suprailiac, and thigh. The protocol is shorter than the 7-site version, which makes it easier to repeat consistently when you are tracking change over time.

This method is often used when you want a portable, low-cost estimate and do not need a lab-based measurement. Like any skinfold equation, the result is an estimate that depends heavily on measurement technique.

When This Page Helps

This page is useful when you want a quick caliper-based estimate that is easier to repeat than the longer 7-site protocol. It can give more body-composition context than body weight or BMI alone, especially when the same person uses the same technique each time.

How to Use the Inputs

1. Select your sex to determine the correct measurement sites.
2. Enter your age (the formula is age-adjusted).
3. Men: measure chest, abdomen, and thigh skinfolds with calipers.
4. Women: measure triceps, suprailiac, and thigh skinfolds with calipers.
5. Enter each skinfold measurement in millimeters.
6. Optionally enter weight to see fat mass and lean mass breakdown.

Example Calculation

Tips & Best Practices

• Always pinch on the right side of the body for standardization.
• Take each measurement 2-3 times to the nearest 0.5 mm and average them.
• Read the caliper 1-2 seconds after releasing the trigger — waiting longer gives artificially low readings.
• The skinfold should be a vertical fold except: chest (diagonal), suprailiac (diagonal). Thigh, triceps, and abdomen are vertical.
• Don't measure immediately after exercise — blood flow to skin changes skinfold thickness.
• Consistent tester technique matters more than caliper brand. Have the same person measure each time.

3-Site vs. 7-Site Skinfold Testing

The 3-site test is faster and easier, while the 7-site test captures more detail across the body. In practice, the 3-site formula is within 1% of the 7-site for most people. The 7-site is preferred in research settings and when you need maximum accuracy. The 3-site is better for frequent tracking and when time is limited.

Measurement Site Descriptions

Chest (men): diagonal fold, midway between the anterior axillary line and nipple. Abdomen (men): vertical fold, 2 cm to the right of the umbilicus. Thigh (both): vertical fold on the anterior midline of the thigh, midway between proximal border of the patella and inguinal crease. Triceps (women): vertical fold on the posterior midline of the upper arm, midway between acromion and olecranon. Suprailiac (women): diagonal fold, above the iliac crest at the anterior axillary line.

Frequently Asked Questions

• Which sites do men and women measure?

  Men measure chest (pectoral, diagonal fold midway between armpit and nipple), abdomen (vertical fold 1 inch to the right of the navel), and thigh (vertical fold midway between hip and knee on the front of the thigh). Women measure triceps (vertical fold on the back of the upper arm), suprailiac (diagonal fold above the hip bone), and thigh (same as men). These specific sites were validated by Jackson and Pollock in their original research.

• How accurate is the 3-site skinfold test?

  The Jackson-Pollock 3-site formula has a standard error of estimate of about 3.5% body fat compared to hydrostatic weighing. In practice, with a skilled tester, you can expect results within ±3-4% of DEXA. The key factors affecting accuracy are tester experience, consistent technique, and caliper quality. Repeated measurements by the same tester improve reliability.

• What type of calipers should I use?

  For clinical accuracy, Harpenden or Lange calipers ($200-400) are the standard. For personal use, Slim Guide ($25) or AccuMeasure ($10) calipers provide acceptable accuracy. The most important factor is consistent jaw pressure (10 g/mm²) and reading technique. Cheap plastic calipers from Amazon vary significantly in jaw pressure and should be avoided for tracking purposes.

• Why does age matter in the formula?

  Body density changes with age independently of skinfold thickness. As people age, internal (visceral) fat increases even if subcutaneous fat stays the same. Bone density also decreases with age, affecting overall body density. The age correction term accounts for these changes, making the formula more accurate across different age groups.

• What is the Siri equation?

  The Siri equation converts body density to body fat percentage: BF% = (495 / density) − 450. It assumes fat density = 0.900 g/cm³ and fat-free mass density = 1.100 g/cm³. An alternative, the Brozek equation ((457 / density) − 414.2), gives slightly different results. The Siri equation is the standard in Jackson-Pollock methodology. Both assume a two-compartment model (fat vs. fat-free mass).

• Can I use the 3-site test to track progress over time?

  Absolutely — this is one of its best uses. Even if the absolute body fat estimate has some error, tracking changes over time is very reliable when the same person measures with the same technique. The sum of skinfolds alone (without plugging into the formula) is an excellent progress metric. A decrease from 50 mm to 40 mm clearly indicates fat loss regardless of the converted percentage.