Coleman–Liau Index calculator
Calculate the Coleman-Liau readability index. Paste text below; your Coleman–Liau Index score is highlighted alongside the other formulas.
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The Coleman–Liau Index formula
CLI = 0.0588 × L − 0.296 × S − 15.8 (L = letters per 100 words, S = sentences per 100 words)
It combines:
- Average number of letters per 100 words
- Average number of sentences per 100 words
Where it came from
Meri Coleman and T. L. Liau published the index in 1975. They wanted a formula a machine could calculate easily, since counting letters is far more reliable for a computer than counting syllables.
When to use it
Automated checking of large amounts of text, and texts where syllable counting is unreliable (lots of names, abbreviations or technical terms).
Watch out for
Letter counts treat all long words alike, so a text with many long but familiar words (like “understanding”) can score harder than it reads.
Reading the grade
| Score | Reader |
|---|---|
| 1–5 | Primary school, age 6–11 |
| 6–8 | Middle school, age 11–14: general public |
| 9–12 | High school, age 14–18 |
| 13–16 | College |
| 17+ | Graduate / professional |
Other formulas
Flesch Reading Ease & Flesch-Kincaid · Gunning Fog Index · SMOG Index · Automated Readability Index
Questions people ask
Why does Coleman–Liau use letters instead of syllables?
Letters can be counted exactly by software, while syllable counts are estimates. Coleman and Liau found letters per word predicted difficulty about as well as syllables.
What is a good Coleman–Liau score?
Like other grade formulas, 8 or below suits the general public, 9–12 suits high-school and general adult reading, and 13+ is college level.
Is Coleman–Liau the same as ARI?
No, though both use characters rather than syllables. ARI uses characters per word and words per sentence with different weights, so the two usually differ by a grade or so.