Coleman-Liau Index
The Coleman-Liau Index is a readability metric used to indicate how difficult a text is to read based on the number of letters per word and words per sentence. Unlike most of the other indices, Coleman-Liau relies on characters instead of syllables per word because characters are more readily and accurately counted by computer programs than syllables.
Values correspond to the number of years of education a reader requires in order to understand a text. For example, a value of 6 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 tends to return lower values as compared to other readability formulae.
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 relative readablity 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:
- Time to Read Metric
- Flesch Reading Ease
- Flesch-Kincaid Grade Level
- Gunning Fog Index
- Automated Readability Index
- SMOG Index
- Linsear Write
- New Dale-Chall Score
- FORCAST Grade
- Average Grade