{
  "id": "fog",
  "version": "77a2e14387ac",
  "status": "published",
  "name": "Fog Calculator",
  "question": "What is my Gunning fog index?",
  "summary": "A fog calculator for the Gunning fog index: paste a text, or type its word, sentence and complex word counts, to estimate the years of schooling a reader needs.",
  "category": "everyday-life",
  "subcategory": "fun",
  "url": "https://www.acalculator.org/everyday-life/fog-calculator",
  "markdown": "https://www.acalculator.org/everyday-life/fog-calculator.md",
  "kind": "function",
  "method": "Fog index = 0.4 × (words ÷ sentences + 100 × complex words ÷ words); a complex word has 3 or more syllables.",
  "assumptions": [
    "From text, syllables are counted by vowel groups, which is close to, but not the same as, counting them by ear.",
    "Hyphenated words, names (a capital letter not at the start of a sentence) and syllables added by -es, -ed or -ing do not make a word complex.",
    "The index assumes whole sentences of ordinary prose; lists, code and headings skew it."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "from": {
        "title": "I have",
        "description": "A text to paste, or the counts of words, sentences and complex words.",
        "type": "string",
        "enum": [
          "text",
          "counts"
        ]
      },
      "t": {
        "title": "Your text",
        "description": "Paste a passage of about 100 words or more, in whole sentences.",
        "type": "string",
        "maxLength": 20000
      },
      "w": {
        "title": "Words",
        "description": "The number of words in the passage.",
        "type": "integer",
        "minimum": 1,
        "maximum": 1000000000
      },
      "s": {
        "title": "Sentences",
        "description": "The number of sentences in the passage.",
        "type": "integer",
        "minimum": 1,
        "maximum": 1000000000
      },
      "c": {
        "title": "Complex words",
        "description": "Words of three or more syllables, as Gunning counts them.",
        "type": "integer",
        "minimum": 0,
        "maximum": 1000000000
      }
    }
  },
  "outputs": {
    "fog": {
      "label": "Fog index",
      "description": "0.4 × (words per sentence + percent complex words).",
      "format": "number"
    },
    "perSentence": {
      "label": "Words per sentence",
      "description": "Words ÷ sentences.",
      "format": "number"
    },
    "percentComplex": {
      "label": "Complex words",
      "description": "Complex words ÷ words × 100, in percent.",
      "format": "number"
    },
    "wordCount": {
      "label": "Words",
      "description": "Words counted.",
      "format": "integer"
    },
    "sentenceCount": {
      "label": "Sentences",
      "description": "Sentences counted.",
      "format": "integer"
    },
    "complexCount": {
      "label": "Complex words counted",
      "description": "Words of 3 or more syllables.",
      "format": "integer"
    },
    "complexList": {
      "label": "Complex words found",
      "description": "The complex words in the text, in order, each once (up to 30).",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "from": "text",
      "t": "The fog index estimates the years of schooling a reader needs to follow a text on the first reading. Short sentences and plain words keep the number low. Long sentences full of complicated terminology push it higher, sometimes beyond the level of a university graduate.",
      "w": 100,
      "s": 5,
      "c": 10
    },
    "outputs": {
      "fog": 10.444444444444445,
      "perSentence": 15,
      "percentComplex": 11.11111111111111,
      "wordCount": 45,
      "sentenceCount": 3,
      "complexCount": 5,
      "complexList": "estimates, complicated, terminology, sometimes, university"
    },
    "text": "The passage has a Gunning fog index of 10.4: 45 words in 3 sentences."
  },
  "examples": [
    {
      "given": {
        "from": "counts",
        "w": 100,
        "s": 5,
        "c": 10
      },
      "expect": {
        "fog": 12,
        "perSentence": 20,
        "percentComplex": 10
      },
      "source": "Gunning fog index, Wikipedia (0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]; complex words have three or more syllables, not counting proper nouns, familiar jargon, compound words, or the common suffixes -es, -ed and -ing; Robert Gunning, The Technique of Clear Writing, McGraw-Hill, 1952), https://en.wikipedia.org/wiki/Gunning_fog_index (retrieved 2026-10-03); hand calculation in content.mdx: 0.4 × (100 ÷ 5 + 100 × 10 ÷ 100) = 0.4 × 30 = 12"
    },
    {
      "given": {
        "from": "counts",
        "w": 230,
        "s": 14,
        "c": 21
      },
      "expect": {
        "fog": 10.22360248447205,
        "perSentence": 16.428571428571427,
        "percentComplex": 9.130434782608695
      },
      "source": "Gunning fog index, Wikipedia (0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]; complex words have three or more syllables, not counting proper nouns, familiar jargon, compound words, or the common suffixes -es, -ed and -ing; Robert Gunning, The Technique of Clear Writing, McGraw-Hill, 1952), https://en.wikipedia.org/wiki/Gunning_fog_index (retrieved 2026-10-03); hand calculation in content.mdx: 230 ÷ 14 = 16.43; 2,100 ÷ 230 = 9.13; 0.4 × 25.56 = 10.22, shown 10.2"
    },
    {
      "given": {
        "from": "text",
        "t": "Communication is important. Anna and Michael understand everything. We tested the well-organized interface."
      },
      "expect": {
        "wordCount": 13,
        "sentenceCount": 3,
        "complexCount": 5,
        "complexList": "communication, important, understand, everything, interface"
      },
      "source": "Gunning fog index, Wikipedia (0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]; complex words have three or more syllables, not counting proper nouns, familiar jargon, compound words, or the common suffixes -es, -ed and -ing; Robert Gunning, The Technique of Clear Writing, McGraw-Hill, 1952), https://en.wikipedia.org/wiki/Gunning_fog_index (retrieved 2026-10-03); hand calculation in content.mdx: complex: communication (5), important (3), understand (3), everything (3), interface (3); not Anna, Michael, tested, well-organized"
    }
  ],
  "sources": [
    "Gunning fog index, Wikipedia (0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]; complex words have three or more syllables, not counting proper nouns, familiar jargon, compound words, or the common suffixes -es, -ed and -ing; developed by Robert Gunning in 1952, The Technique of Clear Writing, McGraw-Hill). https://en.wikipedia.org/wiki/Gunning_fog_index (retrieved 2026-10-03)"
  ],
  "related": [
    "word-counter",
    "reading-time",
    "characters-to-words"
  ],
  "changelog": []
}