{
  "slug": "body-fat-3-site",
  "title": "Body Fat Percentage (3-Site Caliper)",
  "category": "Body Composition",
  "category_slug": "body-composition",
  "tier": 2,
  "summary": "Estimate body fat percentage from three skinfold sites using the Jackson-Pollock female-protocol equation.",
  "description": "This calculator estimates body fat percentage using the Jackson-Pollock 3-site skinfold equation (1978/1980), validated on female populations. It requires three skinfold measurements—tricep, suprailiac, and thigh—plus age, then calculates body density and converts it to body fat percentage via the Siri equation. The protocol uses female-specific measurement sites; accurate results depend on proper caliper technique and consistent measurement conditions.",
  "page_url": "https://fitmetriclab.com/en/tools/body-composition/body-fat-3-site/",
  "api_url": "https://fitmetriclab.com/api/tools/body-fat-3-site.json",
  "formula": {
    "id": "body_fat_3_site",
    "expression": "D = 1.0994921 - 0.0009929\\,\\Sigma + 0.0000023\\,\\Sigma^{2} - 0.0001392\\,a, \\quad \\text{BF}\\% = \\frac{495}{D} - 450",
    "variables": [
      {
        "symbol": "t",
        "description": "Tricep skinfold in mm"
      },
      {
        "symbol": "i",
        "description": "Suprailiac skinfold in mm"
      },
      {
        "symbol": "g",
        "description": "Thigh skinfold in mm"
      },
      {
        "symbol": "a",
        "description": "Age in years"
      },
      {
        "symbol": "s",
        "description": "Sex (male/female)"
      }
    ]
  },
  "inputs": [
    {
      "id": "tricep_mm",
      "label": "Tricep Skinfold",
      "type": "number",
      "unit": "mm",
      "default": 15,
      "min": 1,
      "max": 80,
      "step": 0.5
    },
    {
      "id": "suprailiac_mm",
      "label": "Suprailiac Skinfold",
      "type": "number",
      "unit": "mm",
      "default": 15,
      "min": 1,
      "max": 80,
      "step": 0.5
    },
    {
      "id": "thigh_mm",
      "label": "Thigh Skinfold",
      "type": "number",
      "unit": "mm",
      "default": 20,
      "min": 1,
      "max": 80,
      "step": 0.5
    },
    {
      "id": "age",
      "label": "Age",
      "type": "number",
      "unit": "yrs",
      "default": 30,
      "min": 10,
      "max": 100,
      "step": 1
    },
    {
      "id": "sex",
      "label": "Sex",
      "type": "select",
      "unit": null,
      "default": 1,
      "options": [
        {
          "value": 1,
          "label": "Male"
        },
        {
          "value": 0,
          "label": "Female"
        }
      ]
    }
  ],
  "worked_example": {
    "inputs": {
      "tricep_mm": 15,
      "suprailiac_mm": 15,
      "thigh_mm": 20,
      "age": 30,
      "sex": 1
    },
    "expected_output": "20.8%"
  },
  "result_summary_template": "Using skinfold measurements of {tricep_mm} mm at the tricep, {suprailiac_mm} mm at the suprailiac, and {thigh_mm} mm at the thigh, along with an age of {age} years, the Jackson-Pollock 3-site equation estimates body fat percentage at {result}.",
  "methodology": "Jackson-Pollock 3-site (1978/1980) female protocol: body density D = 1.0994921 − 0.0009929×Σ + 0.0000023×Σ² − 0.0001392×age, where Σ = tricep + suprailiac + thigh skinfolds (mm). Converted to BF% via Siri: (495/D) − 450. Validated on female populations; male-site protocol (chest/abdominal/thigh) requires separate tool.",
  "sources": [
    {
      "label": "Jackson AS, Pollock ML. Practical assessment of body composition. Phys Sportsmed. 1985;13(5):76-90.",
      "url": "https://doi.org/10.1080/00913847.1985.11708790"
    },
    {
      "label": "Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Med Sci Sports Exerc. 1980;12(3):175-81.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/7402053/"
    },
    {
      "label": "Siri WE. Body composition from fluid spaces and density. In: Brozek J, Henschel A, editors. Techniques for Measuring Body Composition. Washington, DC: National Academy of Sciences; 1961. p. 223-44.",
      "url": "https://www.ncbi.nlm.nih.gov/books/NBK235970/"
    }
  ],
  "faqs": [
    {
      "question": "Why does this tool use only the female-protocol sites?",
      "answer": "The Jackson-Pollock 3-site method defines sex-specific measurement sites—tricep, suprailiac, and thigh for females; chest, abdominal, and thigh for males. This tool collects the female-protocol sites and applies the corresponding equation. Males measuring these sites will receive an approximation; protocol-validated results require the male sites (chest, abdominal, thigh) and the male-specific equation."
    },
    {
      "question": "How accurate are skinfold calipers compared to DEXA or hydrostatic weighing?",
      "answer": "Skinfold equations predict body density with standard errors of 3–5 % body fat in validation studies. DEXA and hydrostatic weighing measure compartments directly and typically show lower error, but skinfold calipers remain a practical field method when administered by trained testers using consistent technique. Accuracy depends heavily on technician skill and anatomical site identification."
    },
    {
      "question": "What if my skinfold sum exceeds 60 mm?",
      "answer": "Most spring-loaded calipers measure reliably up to 50–80 mm depending on model. Beyond that range, the equation extrapolates outside its validation dataset, and measurement precision declines due to tissue compression and caliper-jaw limitations. Results at higher sums carry greater uncertainty and should be interpreted as rough estimates."
    },
    {
      "question": "How does age affect the body fat calculation?",
      "answer": "The Jackson-Pollock equation includes an age coefficient (−0.0001392 per year) to account for changes in tissue density and fat distribution with aging. For a given skinfold sum, older individuals typically have slightly higher estimated body fat percentages because subcutaneous fat redistributes and intramuscular adipose increases over time."
    },
    {
      "question": "Can I track body fat changes over time with this method?",
      "answer": "Skinfold measurements can reveal trends when technique remains consistent—same tester, same time of day, same hydration status, and same phase of the menstrual cycle for females. Session-to-session variability of 1–2 mm per site is common, so changes smaller than 3–5 % body fat over weeks may fall within measurement noise rather than true physiological shifts."
    }
  ],
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      "slug": "body-fat-7-site",
      "title": "Body Fat Percentage (7-Site Caliper)",
      "api_url": "https://fitmetriclab.com/api/tools/body-fat-7-site.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/body-fat-7-site/"
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    {
      "slug": "body-fat-navy",
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      "api_url": "https://fitmetriclab.com/api/tools/body-fat-navy.json",
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      "title": "Lean Body Mass Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/lean-body-mass.json",
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  ],
  "last_updated": "2026-04-22",
  "price": {
    "value": 0,
    "currency": "USD"
  },
  "runs_in_browser": true,
  "disclaimer": "Educational estimate produced from a published formula. Not medical, nutritional, or training advice. Calculations are deterministic — apply the formula to the inputs to reproduce the result."
}