{
  "id": "ffmi",
  "version": "23af40b7f479",
  "status": "published",
  "name": "FFMI Calculator",
  "question": "What is my FFMI?",
  "summary": "Computes fat-free mass index (lean mass in kg ÷ height in m squared) and the height-normalized FFMI of Kouri et al. (1995) from height, weight, and body fat.",
  "category": "health",
  "subcategory": "body",
  "url": "https://www.acalculator.org/health/ffmi-calculator",
  "markdown": "https://www.acalculator.org/health/ffmi-calculator.md",
  "kind": "function",
  "method": "FFMI = weight × (1 − body fat ÷ 100) ÷ height²; normalized FFMI = FFMI + 6.3 × (1.80 − height), weight in kg, height in m (Kouri et al. 1995).",
  "assumptions": [
    "The result is only as good as the body fat percentage you enter.",
    "The 25.0 reference is the upper limit Kouri et al. (1995) found in 74 male athletes who had not used steroids. There is no matching published limit for women."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "sex": {
        "title": "Sex",
        "description": "Sex at birth. The 25.0 reference applies to men only.",
        "type": "string",
        "enum": [
          "male",
          "female"
        ]
      },
      "height": {
        "title": "Height",
        "description": "Your height without shoes.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.5,
        "maximum": 3
      },
      "weight": {
        "title": "Weight",
        "description": "Your body weight.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "mass",
        "exclusiveMinimum": 0,
        "maximum": 700
      },
      "bodyFat": {
        "title": "Body fat",
        "description": "Your body fat as a percent of body weight, from a scan, calipers, or an estimate.",
        "type": "number",
        "x-unit": "percent",
        "minimum": 2,
        "maximum": 70
      }
    }
  },
  "outputs": {
    "normalized": {
      "label": "Normalized FFMI",
      "description": "FFMI adjusted to a height of 1.80 m: FFMI + 6.3 × (1.80 − height in m) (Kouri et al. 1995).",
      "format": "number"
    },
    "ffmi": {
      "label": "FFMI",
      "description": "Fat-free mass in kg ÷ height in m squared.",
      "format": "number"
    },
    "leanMass": {
      "label": "Fat-free mass",
      "description": "Weight × (1 − body fat ÷ 100).",
      "format": "quantity",
      "unit": "lb"
    },
    "fatMass": {
      "label": "Fat mass",
      "description": "Weight × body fat ÷ 100.",
      "format": "quantity",
      "unit": "lb"
    },
    "reference": {
      "label": "Compared with Kouri et al.",
      "description": "For men: whether the normalized FFMI is within the 25.0 limit of steroid-free athletes in Kouri et al. (1995).",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "sex": "male",
      "height": 1.778,
      "weight": 81.6466266,
      "bodyFat": 15
    },
    "outputs": {
      "normalized": 22.091588915263543,
      "ffmi": 21.952988915263543,
      "leanMass": 69.39963261,
      "fatMass": 12.246993990000007,
      "reference": "Within the 25.0 limit of steroid-free athletes"
    },
    "text": "Your normalized FFMI is 22.09 (FFMI 21.95)."
  },
  "examples": [
    {
      "given": {
        "sex": "male",
        "height": 1.778,
        "weight": 81.6466266,
        "bodyFat": 15
      },
      "expect": {
        "ffmi": 21.952988915263543,
        "normalized": 22.091588915263543,
        "fatMass": 12.24699399,
        "reference": "Within the 25.0 limit of steroid-free athletes"
      },
      "source": "Kouri et al. (1995): lean mass 81.647 × 0.85 = 69.400 kg; 69.400 ÷ 1.778² = 21.95; + 6.3 × (1.80 − 1.778) = 22.09 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "sex": "female",
        "height": 1.65,
        "weight": 60,
        "bodyFat": 25
      },
      "expect": {
        "ffmi": 16.528925619834713,
        "normalized": 17.473925619834713,
        "leanMass": 45
      },
      "source": "Kouri et al. (1995) definition: 60 × 0.75 = 45 kg; 45 ÷ 1.65² = 16.53; + 6.3 × 0.15 = 17.47 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "sex": "male",
        "height": 1.8,
        "weight": 90,
        "bodyFat": 10
      },
      "expect": {
        "ffmi": 25,
        "normalized": 25,
        "reference": "Within the 25.0 limit of steroid-free athletes"
      },
      "source": "Kouri et al. (1995): 81 kg ÷ 1.8² = 25.0, no height correction at 1.80 m; the steroid-free limit is 25.0 inclusive (hand calculation in content.mdx)",
      "tolerance": 1e-12
    },
    {
      "given": {
        "sex": "male",
        "height": 1.7,
        "weight": 95,
        "bodyFat": 8
      },
      "expect": {
        "normalized": 30.872214532871975,
        "reference": "Above the 25.0 limit of steroid-free athletes"
      },
      "source": "Kouri et al. (1995): 95 × 0.92 = 87.4 kg; 87.4 ÷ 1.7² = 30.24; + 6.3 × 0.10 = 30.87 (hand calculation in content.mdx)"
    }
  ],
  "sources": [
    "Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med. 1995;5(4):223-228. https://doi.org/10.1097/00042752-199510000-00003",
    "NIST SP 811 (2008), Appendix B: 1 lb = 0.45359237 kg and 1 in = 0.0254 m exactly."
  ],
  "related": [],
  "changelog": [
    {
      "date": "2026-09-28",
      "note": "Body fat must be at least 2% (essential fat)."
    }
  ]
}