ClickHelp User Manual

Coleman-Liau Index

The Coleman-Liau Index is a readability metric that indicates how difficult a text is to read based on the number of letters per word and words per sentence. Unlike most other indices, Coleman-Liau relies on characters instead of syllables per word because computer programs more readily and accurately count characters than syllables.

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. So, 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 and above 11th grade - college 17 and above Too hard to read for the majority of readers.

When dealing with technical documentation, the Coleman-Liau index returns lower values than other readability formulae.

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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: