The Gunning Fog Index estimates the years of formal education needed to understand a piece of text on first reading.
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The Gunning Fog index was created by Robert Gunning to identify text that is unnecessarily "foggy" or hard to understand.
It combines average sentence length with the percentage of "complex" words — words of 3+ syllables, with allowances for proper nouns, suffixes, and compound words.
A score of 12 corresponds to high-school senior level. Time and Newsweek typically score around 11.
A word of 3 or more syllables, excluding proper nouns, familiar compound words (like "everywhere"), and words made polysyllabic by common suffixes (-ed, -es, -ing).
Aim for under 12 for general audiences. Anything above 16 is considered very difficult to read.
Yes. The Fog index was popularised by Robert Gunning specifically for business and journalistic writing.
Classic 0–100 readability score.
readabilityU.S. grade level for your text.
readabilityHealth & medical text grade level.
readabilityNo syllables needed — just characters.