Coleman-Liau Index Calculator
The Coleman-Liau Index estimates grade level using characters per word — making it uniquely reliable for technical and scientific text. Get your score instantly below.
Breakdown
What Is the Coleman-Liau Index?
How it works
Developed by Meri Coleman and T. L. Liau in 1975, this formula calculates readability using the average number of characters per word and the average number of sentences per 100 words — rather than syllable counts used by most other formulas.
Why characters instead of syllables?
Counting syllables requires linguistic knowledge and can be inconsistent — especially for technical terminology, proper nouns, or non-English words. Characters are objective and countable by any computer program, making the CLI formula highly consistent.
When to use it
The Coleman-Liau Index is particularly useful for evaluating scientific papers, technical documentation, and legal writing — text types where other formulas can produce inconsistent results due to unusual vocabulary.
Coleman-Liau vs Other Readability Formulas
vs Flesch-Kincaid
Both return a grade level, but Flesch-Kincaid uses syllable counts while Coleman-Liau uses character counts. For most general writing, the scores will be similar. For technical text with many acronyms, Coleman-Liau tends to be more reliable.
vs Gunning Fog
Gunning Fog focuses on "complex words" (3+ syllables) as its key variable. Coleman-Liau instead looks at average word length in characters. Neither is definitively better — they measure slightly different aspects of complexity.
Using multiple scores
No single readability formula is perfect. The most reliable approach is to look at several scores together. If multiple formulas agree, you can be more confident in the result. Our main tool calculates all six scores at once.