Gunning Fog Index

The Gunning Fog Index is a readability metric that uses word and sentence length to determine how difficult a text is to read. Index values typically vary from 0 to 20. Values correspond to the number of years of education a reader requires to understand a text. For example, six corresponds to 11-12-year-old readers, while 12 corresponds to 17-18-year-olds. Values should be interpreted as follows:

Value	School level	Student age range	Notes
0-1	Pre-kindergarten - 1st grade	3-7	Basic level for those who just learn to read books.
1-5	1st grade - 5th grade	7-11	Very easy to read.
5-8	5th grade - 8th grade	11-14	A text is considered ideal for average readers.
8-11	8th grade - 11th grade	14-17	Fairly difficult to read.
11-20	11th grade - college	17 and above	Too hard to read for the majority of readers.

Since it's based on the American Education system, school levels and age ranges may be inaccurate for non-English languages. However, it's still possible to compare the relative readability of two topics written in the same language.

If a metric value is zero, make sure that the project language matches the content language and check the punctuation.

Check out the other readeability metrics:

• Flesch-Kincaid Grade Level
• Coleman-Liau Index
• Flesch Reading Ease
• Automated Readability Index
• Linsear Write
• SMOG Index
• FORCAST Grade
• New Dale-Chall Score
• Average Grade

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