What is the Coleman-Liau Index?
The Coleman-Liau Index was developed by linguists Meri Coleman and T. L. Liau in 1975. It measures
text difficulty using letter count per 100 words and sentence count per 100 words. Unlike Flesch-Kincaid
or SMOG, it requires no syllable analysis—just character counts.
Coleman-Liau often produces lower grade estimates than ARI and Flesch-Kincaid when applied to
technical documents. The formula is designed to align with U.S. grade levels from kindergarten
through college.
How the Coleman-Liau Formula Works
Coleman-Liau uses the number of letters per 100 words and the number of sentences per 100 words. No syllables or word lists—just letter and sentence counts. The formula was designed to be as accurate as syllable-based formulas while using only data that is easy to obtain (letters and sentence boundaries). It often produces slightly lower grade estimates than ARI for the same text, so it can be a useful alternative when you want a character-based measure that is less strict.
When to Use the Coleman-Liau Index
Use Coleman-Liau when you want a grade-level estimate without syllable analysis—for example in automated systems or when working with languages where syllable boundaries are unclear. It is popular in research and in some writing tools. If your guideline specifies Flesch-Kincaid or SMOG, use those; otherwise Coleman-Liau is a good choice for a single grade from letter and sentence stats. To compare with all nine formulas, use our Combined Readability Checker.
Industry Guidelines and Targets
Coleman-Liau is less often explicitly mandated than Flesch-Kincaid or SMOG, but the same general targets apply: 8th grade or lower for broad audiences, 6th–8th for health or consumer materials. Use the calculator to see where your text falls. Because Coleman-Liau can give lower grades than ARI for the same passage, you may find it a useful second opinion when ARI seems high.
How to Improve Your Coleman-Liau Score
To lower the grade, use shorter words (fewer letters per word) and shorter sentences (more sentences per 100 words). Replace long words with shorter alternatives and break long sentences into two or three shorter ones. The formula responds to both dimensions. Re-run your text after revisions to see the new grade. Like ARI, Coleman-Liau does not distinguish word difficulty beyond length, so any shortening helps.
How to Use This Calculator
Paste your text into the box at the top and click analyze. You will see your Coleman-Liau score and a grade-level interpretation. No signup required. For stable results use at least 100 words. To see how the same text scores on ARI, Flesch-Kincaid, SMOG, and six other formulas, use the Combined Readability Checker.
Other Readability Tools
Get all nine formulas at once: Combined Readability Checker. Or explore individual calculators: Flesch-Kincaid Grade Level,
SMOG Index,
Gunning Fog Index,
Dale-Chall Readability,
Automated Readability Index,
Linsear Write,
Lix,
Rix,
and the full Readability Calculators hub.
