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The Coleman-Liau Index is a readability index designed by Meri Coleman and T. L. Liau to gauge the understandability of a text. Like the Flesch-Kincaid Grade Level, Gunning-Fog Index, SMOG Index, and Automated Readability Index, its output approximates the U.S. grade level thought necessary to comprehend the text.

Like the ARI but unlike most of the other indices, Coleman-Liau relies on characters instead of syllables per word. Although opinion varies on its accuracy as compared to the syllable/word and complex word indices, characters are more readily and accurately counted by computer programs than are syllables.


To calculate the Coleman-Liau Index:

  1. Divide the number of characters by the number of words, and multiply by 5.89. Call this A.
  2. Take the number of sentences in a fragment of 100 words, and multiply by 0.3. Call this B.
  3. Subtract B from A and subtract 15.8

CLI = 
5.89 \left ( \frac{\mbox{characters}}{\mbox{words}} \right ) - 29.5 \left ( \frac{\mbox{sentences}}{\mbox{words}} \right ) - 15.8


  • Coleman, M.; and Liau, T. L. (1975); A computer readability formula designed for machine scoring, Journal of Applied Psychology, Vol. 60, pp. 283-284

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