{
  "slug": "body-fat-7-site",
  "title": "Body Fat Percentage (7-Site Caliper)",
  "category": "Body Composition",
  "category_slug": "body-composition",
  "tier": 2,
  "summary": "Jackson-Pollock 7-site skinfold body fat percentage from caliper measurements.",
  "description": "Enter the sum of seven skinfold measurements in millimetres, your age, and sex. The calculator applies the sex-specific Jackson-Pollock body density equation, then converts to body fat percentage via the Siri equation. Result updates live.",
  "page_url": "https://fitmetriclab.com/en/tools/body-composition/body-fat-7-site/",
  "api_url": "https://fitmetriclab.com/api/tools/body-fat-7-site.json",
  "formula": {
    "id": "body_fat_7_site",
    "expression": "D = c_0 - c_1 \\Sigma + c_2 \\Sigma^{2} - c_3 a \\quad \\text{(sex-specific JP coefficients)}, \\quad \\text{BF}\\% = \\frac{495}{D} - 450",
    "variables": [
      {
        "symbol": "\\Sigma",
        "description": "Sum of seven skinfolds (chest, midaxillary, tricep, subscapular, abdominal, suprailiac, thigh) in millimetres"
      },
      {
        "symbol": "a",
        "description": "Age in years"
      },
      {
        "symbol": "D",
        "description": "Body density in g/cm³; computed from Σ and age via the sex-specific Jackson-Pollock equation"
      },
      {
        "symbol": "c_0..c_3",
        "description": "Sex-specific coefficients. Male: c₀=1.112, c₁=0.00043499, c₂=0.00000055, c₃=0.00028826. Female: c₀=1.097, c₁=0.00046971, c₂=0.00000056, c₃=0.00012828."
      }
    ]
  },
  "inputs": [
    {
      "id": "skinfold_sum_mm",
      "label": "Sum of Skinfolds",
      "type": "number",
      "unit": "mm",
      "default": 80,
      "min": 10,
      "max": 400,
      "step": 1
    },
    {
      "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": {
      "skinfold_sum_mm": 80,
      "age": 30,
      "sex": 1
    },
    "expected_output": "11.7%"
  },
  "result_summary_template": "With a 7-site skinfold sum of {skinfold_sum_mm} mm at age {age}, the Jackson-Pollock equation estimates body fat at {result}.",
  "methodology": "Jackson-Pollock 7-site skinfold protocol (Jackson & Pollock 1978; Jackson, Pollock & Ward 1980). The seven sites are chest, midaxillary, tricep, subscapular, abdominal, suprailiac, and thigh. The calculator accepts the sum of all seven readings (in mm), computes body density via the sex-specific Jackson-Pollock generalised equation, then converts density to body fat percentage via the Siri equation BF% = (495 / D) − 450. The sex coefficients differ because subcutaneous fat distribution patterns differ systematically between male and female adults. Accuracy versus hydrostatic weighing is reported as ±3-4% for adults aged 18-61; the equation is less accurate at the extremes of body composition and assumes consistent caliper technique (a single operator across measurements is the strongest predictor of trend reliability).",
  "sources": [
    {
      "label": "Jackson AS, Pollock ML. Generalized equations for predicting body density of men. Br J Nutr. 1978;40(3):497-504.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/718832/"
    },
    {
      "label": "Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Med Sci Sports Exerc. 1980;12(3):175-181.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/7402053/"
    },
    {
      "label": "ACSM's Guidelines for Exercise Testing and Prescription (skinfold protocol reference). American College of Sports Medicine.",
      "url": "https://www.acsm.org/education-resources/books"
    }
  ],
  "faqs": [
    {
      "question": "How is the 7-site skinfold sum measured?",
      "answer": "Take three readings at each of the seven sites (chest, midaxillary, tricep, subscapular, abdominal, suprailiac, thigh) with a calibrated caliper, average each site's readings, then add the seven averaged values. Read each pinch at approximately 2 seconds after the caliper is released to allow the skinfold to compress. Use the same caliper and the same measurer across sessions — operator-to-operator variation can shift the result by a few percentage points."
    },
    {
      "question": "Is Jackson-Pollock 7-site more accurate than 3-site?",
      "answer": "Yes, marginally — averaging seven sites instead of three reduces the variance from any single mis-measurement and better samples regional fat distribution. The two equations both report ±3-4% versus hydrostatic weighing on the validation populations, but 7-site is generally preferred in research and athletic monitoring when time permits. 3-site is faster for routine tracking."
    },
    {
      "question": "Why are the male and female equations different?",
      "answer": "Adult males and females show systematically different patterns of subcutaneous fat distribution at the same total body fat percentage — more central and android in males, more gluteofemoral and gynoid in females. The Jackson-Pollock equations were derived separately for each sex from hydrostatic weighing validation samples to absorb this difference. Applying the male equation to a female (or vice versa) produces a result that is internally consistent but systematically biased."
    },
    {
      "question": "How precise should the skinfold sum input be?",
      "answer": "Each individual skinfold reading is conventionally recorded to the nearest 0.5 mm, but the sum is entered as a whole number here (the JP equation is calibrated against measurements summed to 1 mm). Small differences in the sum produce small differences in the final BF% — a 5 mm change in the sum typically shifts BF% by about 0.5%."
    },
    {
      "question": "Can I track body fat change over time with this tool?",
      "answer": "Yes — and tracking change is more reliable than absolute single measurements, because operator and technique noise mostly cancels when the same person measures the same sites the same way each session. Track the skinfold sum and BF% from this tool at fixed intervals (e.g. every 4-6 weeks) and look for trends across 3+ data points rather than reacting to single readings. Variation under ±0.5% between sessions is typically within measurement noise."
    }
  ],
  "related_tools": [
    {
      "slug": "body-fat-3-site",
      "title": "Body Fat Percentage (3-Site Caliper)",
      "api_url": "https://fitmetriclab.com/api/tools/body-fat-3-site.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/body-fat-3-site/"
    },
    {
      "slug": "body-fat-navy",
      "title": "Body Fat Percentage (Navy Method)",
      "api_url": "https://fitmetriclab.com/api/tools/body-fat-navy.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/body-fat-navy/"
    },
    {
      "slug": "lean-body-mass",
      "title": "Lean Body Mass Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/lean-body-mass.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/lean-body-mass/"
    }
  ],
  "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."
}