7-Site Skinfold Body Fat Calculator
Enter the sum of your 7 skinfold measurements, age and sex.
Result
How it is calculated
The sum S of your seven skinfold readings in millimetres is turned into body density with a quadratic Jackson-Pollock equation. For men: BD = 1.112 − 0.00043499·S + 0.00000055·S² − 0.00028826·age. For women: BD = 1.097 − 0.00046971·S + 0.00000056·S² − 0.00012828·age. Body fat then follows from the Siri formula: % fat = 495 ÷ BD − 450.
The result is placed in a band that depends on sex. For men: below 6% essential fat, 6–14 athletes, 14–18 fitness, 18–25 average, 25 and above obese. For women the cut-offs are 14, 21, 25 and 32. Sum and age must be above zero. Density is shown to five decimals and body fat to one. The equation is a regression estimate, so a measurement error of a few millimetres moves the result by a percentage point or more.
Worked example
A 30-year-old man has a seven-site sum of 120 mm. Terms: 0.00043499 × 120 = 0.05220; 0.00000055 × 120² = 0.00792; 0.00028826 × 30 = 0.00865. Body density = 1.112 − 0.05220 + 0.00792 − 0.00865 = 1.05907 g/cm³. Body fat = 495 ÷ 1.05907 − 450 = 17.4%, which falls in the Fitness band for men (14 to under 18%). A woman with the same sum and age would get 23.8%, because the equation and bands differ by sex.
Common mistakes
- Entering one skinfold reading instead of the sum of all seven. A single value of 18 mm gives an absurdly low body fat.
- Entering skinfolds in centimetres or inches. The sum must be in millimetres.
- Selecting the wrong sex. The equations differ, and the same sum gives a noticeably higher percentage for women.
- Pinching inconsistently, with different pressure, a different spot or on different days. The result depends on technique, so use the same person and the same sites to track changes.
- Treating one figure as exact. Use it to follow the trend over weeks, not as a single precise reading.
About this calculator
The Jackson-Pollock 7-site skinfold method estimates body fat percentage by measuring the thickness of skin folds — using calipers — at seven standardized locations on the body (chest, midaxillary, triceps, subscapular, abdomen, suprailiac, and thigh), since the thickness of subcutaneous fat at these sites correlates with total body fat. The sum of the seven measurements, combined with age and sex, is plugged into a regression equation developed by researchers Jackson and Pollock to estimate body density, which then converts to a body fat percentage.
This calculator applies that equation to your seven-site skinfold sum, age, and sex. It's a long-standing method used by personal trainers, strength coaches, and exercise physiologists for tracking body composition changes over time — it's more accurate than simple BMI-based estimates and doesn't require specialized equipment like a DEXA scan, though results depend heavily on measurement technique and are best used to track trends rather than as a single precise reading.
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