Coleman-Liau index calculator
The Coleman-Liau Index calculates readability without counting syllables. It uses characters per word and sentences per 100 words — making it more reliable for technical content and code-adjacent text.
- No syllable counting — character-based
- Reliable for technical and code-adjacent text
- Output: US grade level
- Free, no signup
The formula
Coleman-Liau = 0.0588 × L − 0.296 × S − 15.8Where L = average letters per 100 words and S = average sentences per 100 words. Output is a US grade level.
The key insight: characters per word is a reasonable proxy for syllables per word, but it can be counted mechanically with zero ambiguity. Syllable counting requires heuristics that break on proper nouns, abbreviations, and code.
When Coleman-Liau wins
- Technical documentation. API docs, SDK guides, and developer content often contain abbreviations and code that syllable counters mishandle.
- Content with lots of proper nouns.Tech, sports, and political writing — syllable heuristics over-count or under-count these in unpredictable ways.
- Machine-translated or AI-generated text. Often has odd phrasing that fools syllable counters but is correctly graded by character counts.
Coleman-Liau vs syllable-based formulas
On clean narrative prose, Coleman-Liau usually agrees with Flesch- Kincaid within 1 grade. The differences become visible on:
- Texts with many short Latin words— Coleman- Liau may rate them as easier than Flesch does.
- Compound-noun-heavy text— Coleman-Liau may rate as harder (because compound words are character-dense even when comprehensible).
- Lists and headings— both formulas struggle, but Coleman-Liau is more stable.
Score interpretation
Same scale as other US-grade formulas. Roughly:
- Grade 5–6:Children’s books, marketing copy
- Grade 7–9: Newspapers, magazines, most successful blogs
- Grade 10–12: Professional writing, business content
- Grade 13+: Academic, technical, specialist
Practical tip: cross-reference with Flesch
For most editing work, running both Coleman-Liau and Flesch-Kincaid on the same text reveals more than either alone. If they agree closely, trust the result. If they diverge by 3+ grades, your text has unusual character/syllable ratios — investigate the longest words and check whether they’re actually hard or just dense.