Body Fat Calculator (7-Site Skinfold)

About the Body Fat Calculator (7-Site Skinfold)

The Jackson-Pollock 7-site skinfold test is one of the more detailed caliper-based methods for estimating body fat percentage. By measuring seven locations, it captures a broader picture of subcutaneous fat distribution than shorter protocols.

The seven measurements are chest, midaxillary, triceps, subscapular, abdomen, suprailiac, and thigh. Their sum is entered into a sex-specific body-density equation and then converted to body fat percentage with the Siri formula.

This method is commonly used in exercise-science settings when someone wants a repeatable field estimate without relying on lab equipment. Like any skinfold equation, the output is only as good as the measurement technique behind it.

When This Page Helps

This version is useful when you want a more detailed caliper estimate and are willing to take extra measurements. Spreading the estimate across seven sites can reduce the influence of one bad pinch and gives a fuller field-based check than the shorter 3-site method.

How to Use the Inputs

1. Select your sex (both sexes use the same 7 sites but different equations).
2. Enter your age.
3. Measure all 7 skinfold sites with calipers (in millimeters).
4. Sites: chest, midaxillary, triceps, subscapular, abdomen, suprailiac, thigh.
5. Optionally enter weight for fat mass and lean mass breakdown.
6. View your body density, body fat %, and classification.

Example Calculation

Tips & Best Practices

• Measure on the right side of the body for all 7 sites. This is the standardized protocol.
• Take each skinfold measurement at least 2 times and average. If readings differ by more than 2 mm, take a third.
• Pinch the skinfold 1 cm above the measurement site, then place the caliper jaws AT the site.
• Read calipers 1-2 seconds after releasing the trigger. Waiting longer gives compressed (lower) readings.
• The subscapular and chest folds are diagonal; triceps, abdomen, and thigh are vertical; suprailiac is diagonal; midaxillary is vertical.
• Don't measure after exercise or sauna — skin hydration affects readings.
• Practice on different body types to improve inter-test consistency.

Jackson-Pollock 7-Site Research

The original validation studies included 308 men (Jackson & Pollock, 1978) and 249 women (Jackson, Pollock & Ward, 1980). Participants ranged from 18-61 years old. Body density was measured via hydrostatic (underwater) weighing, then regression equations were derived. The equations have been cross-validated in multiple populations and remain the standard after 45+ years.

When to Choose 7-Site Over 3-Site

Choose the 7-site test when: you're doing a baseline assessment, accuracy matters more than speed, you have an experienced tester, or you want site-specific fat distribution data. Choose the 3-site test when: time is limited, self-measuring, or tracking frequent progress checks (weekly).

Frequently Asked Questions

• What are the 7 measurement sites?

  Chest: diagonal fold between armpit and nipple. Midaxillary: vertical fold on the midaxillary line at xiphoid (breastbone) level. Triceps: vertical fold on the back of the upper arm, halfway between shoulder and elbow. Subscapular: diagonal fold 1-2 cm below the inferior angle of the scapula. Abdomen: vertical fold 2 cm right of the navel. Suprailiac: diagonal fold above the iliac crest at the anterior axillary line. Thigh: vertical fold on the front of the thigh, midway between hip and knee.

• How much more accurate is the 7-site vs. the 3-site test?

  In most studies, the difference is small: the 7-site has a standard error of estimate of about 3.4% vs. 3.5% for the 3-site. However, the 7-site test is more robust to individual measurement errors because no single site carries disproportionate weight. It also better captures unusual fat distribution patterns. For most people, the practical difference is minimal.

• Can I track progress with just the sum of skinfolds?

  Absolutely. The sum of 7 skinfolds (in mm) is itself an excellent metric for tracking body composition changes. A decrease in the total sum reliably indicates fat loss, regardless of the formula-calculated percentage. Many strength coaches track the raw sum and individual site measurements over time for a detailed picture of where fat is being lost.

• What's the Siri equation and why is it used?

  The Siri equation (BF% = 495/density − 450) converts body density to body fat percentage using a two-compartment model. It assumes fat tissue has a density of 0.900 g/cm³ and fat-free tissue 1.100 g/cm³. It was published by William Siri in 1961 and is the standard conversion used with Jackson-Pollock equations. For populations with very different bone density (e.g., elderly, some ethnicities), the Brozek equation may be more appropriate.

• Do I need a partner to measure all 7 sites?

  Realistically, yes. The subscapular (below shoulder blade) and midaxillary sites are very difficult to measure on yourself accurately. While chest, abdomen, suprailiac, triceps, and thigh can be self-measured with practice, having a trained partner or professional ensures better accuracy and repeatability, especially for the hard-to-reach sites.

• Why is the same formula not used for men and women?

  Men and women store fat differently due to hormonal influences. Women have higher essential fat (for reproductive function), more subcutaneous fat in the lower body, and different relationships between skinfold thickness and total body fat. The separate equations account for these sex-specific fat distribution patterns to produce more accurate estimates for each sex.