Estimate the U.S. grade level needed to understand the text using character and word counts. Fast and reliable.
Use Coleman–Liau when you need a robust automated score — it has no syllable counter, so it cannot be tripped up by unusual words or foreign names. It is the safest choice for OCR’d text, social-media posts, or content with lots of proper nouns.
Coleman–Liau and ARI both rely on character counts and typically produce similar grade levels. Compared to Flesch–Kincaid, they are more robust to unusual vocabulary but blind to word familiarity. Use Coleman–Liau when automating; use FK when communicating with humans who already know it.
The Coleman-Liau index was designed in 1975 specifically for automated computing — it requires no syllable counting.
It uses characters per word and sentences per 100 words to estimate US grade level.
Because it only needs character counts, it generalises better across languages with regular spelling.
Characters are easier to count programmatically and don't require language-specific syllable rules. This makes Coleman-Liau a popular choice for automated tools.
Yes — Coleman-Liau correlates well with cloze test scores, the gold standard of readability research.
L is the average number of letters per 100 words and S is the average number of sentences per 100 words. The result is a U.S. grade level, so a score of 9 means the text suits a ninth-grade reader.
Coleman-Liau judges word difficulty by letter count while Flesch-Kincaid uses syllables, so a text full of short but multi-syllable words can score differently. For most prose the two land within a grade or two of each other.
Input
Coleman–Liau needs no syllable count. It uses letters and sentences.
Output
Coleman–Liau Index: 8.5 — 8th–9th grade.
About 4.6 letters per word and ~7 words per sentence. The character-based formula handles the punctuation and lengths directly, no syllable counting required.
Classic 0–100 readability score.
readabilityU.S. grade level for your text.
readabilityPenalises complex (3+ syllable) words.
readabilityHealth & medical text grade level.