Gunning Fog Index Calculator

Gunning Fog Index calculator

The Gunning Fog Index estimates the years of formal education a reader needs to understand text on first reading. Gunning suggested that most business writing should stay under 12, and that popular magazines sat around 10.

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Gunning Fog Index

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Readability scores for your text
Formula	Score	Reads as
Flesch Reading Ease	–
Flesch-Kincaid Grade	–	–
Gunning Fog	–	–
SMOG	–	– *
Coleman-Liau	–	–
Automated Readability	–	–
Dale-Chall	–

Formula

Score

Reads as

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Coleman-Liau

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Automated Readability

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Dale-Chall

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The Gunning Fog Index formula

Fog = 0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]

Average sentence length
Percentage of complex words (three or more syllables)

What it counts

Complex words are those with three or more syllables. Following Gunning, this calculator does not count proper nouns, hyphenated compounds, or words that only reach three syllables by adding -es, -ed or -ing (so “created” counts, but “reported” does not).

What score to aim for

Under 12 for broad audiences; around 8 for content anyone should grasp. Scores over 17 read like postgraduate text. Targets by audience are collected in what is a good readability score, and the reading level chart maps every grade to an age and a Flesch band.

Limits to keep in mind

Some long words are easy (“everybody”, “interesting”) and some short words are hard (“gnomic”). Fog treats them all by length.

Where it comes from

Robert Gunning, a consultant to newspapers and businesses, introduced the index in his 1952 book on clear writing. The name comes from the “fog” of long words and sentences.

Source: Gunning, R. (1952). The Technique of Clear Writing. New York: McGraw-Hill.

How we count syllables, sentences and words, and how our numbers compare on test passages, is documented in Readability formulas explained.

Gunning Fog Index: common questions

What is a good Gunning Fog score?

Around 7–8 reads easily for almost anyone; 12 or below suits most business and web writing. Anything above 17 is very demanding.

What counts as a complex word in the Fog Index?

A word of three or more syllables, excluding proper nouns, familiar jargon, hyphenated compounds, and words made three-syllable only by -es, -ed or -ing. Jargon is not detectable automatically, so the jargon exclusion is not applied here.

How is the Fog Index different from Flesch-Kincaid?

Fog counts the share of long words, while Flesch-Kincaid counts average syllables across all words. Fog is more sensitive to a scattering of long terms in otherwise simple text.

Why is my Fog score higher here than in another tool?

Some tools skip Gunning’s exclusions or count syllables differently. Others count every three-syllable word, which raises the score. We show which words we counted so you can check.

Complex words counted by Fog

The same text, every formula

Formula lab: move the inputs, watch the score