fog indexn.
/ˈfɒɡ ˌɪndɛks/, U.S. /ˈfɔɡ ˌɪnˌdɛks/, /ˈfɑɡ ˌɪnˌdɛks/ Linguistics.
Also more fully Gunning fog index. A measure of the readability of a piece of English-language text, expressed as the number of years of formal education thought to be needed to understand the text.The fog index was developed by the American writing consultant Robert Gunning (1908–80). It is calculated by taking a passage of around 100 words, adding the average number of words in a sentence to the percentage of words having three or more syllables, and multiplying the result by 0.4.
ΚΠ
1945 Journalism Q. 22 270/2 The ‘marks of readable style’ singled out by Dr. Flesch—sentence pattern, ‘fog index’, and human interest—differ little from the ‘clearness, conciseness, and originality’ stressed by all reporting texts.
1952 N.Y. Times Bk. Rev. 24 Feb. 27/3 (advt.) Much writing today is heavy with ‘fog’ and wasted words... The ‘Fog Index’ provides a practical yardstick for measuring your writing.
1987 R. A. Thompson & L. S. Thompson Egoshell ii. C-xii. 267 Based on the number of long words and average sentence length, the fog index identifies the number of school years needed to comprehend a passage being tested.
1998 N. Campbell Writing Effective Policies & Procedures iv. 96 To calculate reading level manually, use the Gunning Fog Index.
2012 J. F. Alexander Being Church ii. 13 If you want modern people to read your work, your fog index better not be any higher than eight.
This is a new entry (OED Third Edition, December 2016; most recently modified version published online March 2022).
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