{
  "id": "pf-ratio",
  "version": "9af1336777ab",
  "status": "published",
  "name": "PF Ratio Calculator",
  "question": "What is the PF ratio?",
  "summary": "Divides the arterial oxygen pressure (PaO2) by the inspired oxygen fraction (FiO2) to give the PF ratio, and shows the Berlin Definition range it falls in.",
  "category": "health",
  "subcategory": "clinical",
  "url": "https://www.acalculator.org/health/pf-ratio-calculator",
  "markdown": "https://www.acalculator.org/health/pf-ratio-calculator.md",
  "kind": "function",
  "method": "PF ratio = PaO2 (mmHg) ÷ (FiO2 % ÷ 100), to a whole mmHg. PaO2 in kPa ÷ 0.133322 = mmHg. Berlin Definition: over 200 to 300 mild, over 100 to 200 moderate, 100 or less severe.",
  "assumptions": [
    "PaO2 and FiO2 are taken at the same time.",
    "The ratio is worked from the exact typed values and rounded once, halves up; the range is read from the whole mmHg value shown.",
    "The Berlin ranges apply only with PEEP or CPAP of 5 cm H2O or more and the other ARDS criteria; the page does not check those."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "units": {
        "title": "PaO2 units",
        "description": "The unit of the blood gas PaO2: mmHg or kPa.",
        "type": "string",
        "enum": [
          "mmhg",
          "kpa"
        ]
      },
      "pao2": {
        "title": "PaO2 (mmHg)",
        "description": "Arterial partial pressure of oxygen from a blood gas, 20 to 700 mmHg.",
        "type": "number",
        "minimum": 20,
        "maximum": 700
      },
      "pao2Kpa": {
        "title": "PaO2 (kPa)",
        "description": "Arterial partial pressure of oxygen from a blood gas, 2.7 to 93.3 kPa.",
        "type": "number",
        "minimum": 2.7,
        "maximum": 93.3
      },
      "fio2": {
        "title": "FiO2",
        "description": "Fraction of inspired oxygen, from 21% (room air) to 100%.",
        "type": "number",
        "x-unit": "percent",
        "minimum": 21,
        "maximum": 100
      }
    }
  },
  "outputs": {
    "pf": {
      "label": "PF ratio (mmHg)",
      "description": "PaO2 in mmHg ÷ FiO2 as a fraction, to a whole number.",
      "format": "number"
    },
    "pfKpa": {
      "label": "PF ratio (kPa)",
      "description": "The same ratio with PaO2 in kPa, to 1 decimal.",
      "format": "number"
    },
    "range": {
      "label": "Berlin Definition range",
      "description": "The oxygenation range of the 2012 Berlin Definition of ARDS that holds the ratio.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "units": "mmhg",
      "pao2": 80,
      "pao2Kpa": 10.7,
      "fio2": 40
    },
    "outputs": {
      "pf": 200,
      "pfKpa": 26.7,
      "range": "Moderate range (over 100, up to 200)"
    },
    "text": "The PF ratio is 200 mmHg (26.7 kPa): Moderate range (over 100, up to 200)."
  },
  "examples": [
    {
      "given": {
        "units": "mmhg",
        "pao2": 80,
        "fio2": 40
      },
      "expect": {
        "pf": 200,
        "pfKpa": 26.7,
        "range": "Moderate range (over 100, up to 200)"
      },
      "source": "Berlin Definition 2012: 80 ÷ 0.40 = 200, moderate (100 < PF ≤ 200) (hand calculation in content.mdx)"
    },
    {
      "given": {
        "units": "mmhg",
        "pao2": 95,
        "fio2": 21
      },
      "expect": {
        "pf": 452,
        "pfKpa": 60.3,
        "range": "Over 300 (above the ARDS ranges)"
      },
      "source": "95 ÷ 0.21 = 452.4 on room air (hand calculation in content.mdx)"
    },
    {
      "given": {
        "units": "mmhg",
        "pao2": 90,
        "fio2": 30
      },
      "expect": {
        "pf": 300,
        "range": "Mild range (over 200, up to 300)"
      },
      "source": "90 ÷ 0.30 = 300, mild (200 < PF ≤ 300, Berlin Definition) (hand calculation)"
    },
    {
      "given": {
        "units": "mmhg",
        "pao2": 60,
        "fio2": 60
      },
      "expect": {
        "pf": 100,
        "pfKpa": 13.3,
        "range": "Severe range (100 or less)"
      },
      "source": "60 ÷ 0.60 = 100, severe (PF ≤ 100, Berlin Definition) (hand calculation in content.mdx)"
    },
    {
      "given": {
        "units": "kpa",
        "pao2Kpa": 10.7,
        "fio2": 50
      },
      "expect": {
        "pf": 161,
        "pfKpa": 21.4,
        "range": "Moderate range (over 100, up to 200)"
      },
      "source": "10.7 kPa ÷ 0.133322 = 80.257 mmHg; ÷ 0.50 = 160.5 mmHg; 10.7 ÷ 0.50 = 21.4 kPa (hand calculation in content.mdx)"
    }
  ],
  "sources": [
    "ARDS Definition Task Force; Ranieri VM, Rubenfeld GD, Thompson BT, et al. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307(23):2526-2533. https://doi.org/10.1001/jama.2012.5669 (retrieved 2026-10-05)",
    "Taylor BN, Thompson A. NIST Special Publication 811: Guide for the Use of the International System of Units, appendix B.8 (1 mmHg = 133.322 Pa). https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-05)"
  ],
  "related": [
    "abg"
  ],
  "changelog": [
    {
      "date": "2026-10-05",
      "note": "Published after this site's editorial review against the cited sources (no clinician review); the page notices say so."
    }
  ]
}