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Coleman-Liau Index Calculator Calculate the Coleman-Liau readability index using character-based analysis.

Coleman-Liau Index illustration
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Coleman-Liau Index

Calculate the Coleman-Liau readability index using character-based analysis.

1

Input Your Text

Paste or type the text you want to analyze.

2

View the CLI Score

Get the Coleman-Liau Index score and estimated U.S. grade level.

3

Check Statistics

Review letter counts, sentence counts, and per-100-word ratios.

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What Is Coleman-Liau Index?

The Coleman-Liau Index (1975) uses character counts instead of syllable counts for deterministic readability measurement. Formula: 0.0588*L - 0.296*S - 15.8, where L = average letters per 100 words and S = average sentences per 100 words. Because counting characters is unambiguous, results are perfectly reproducible. The formula correlates strongly with syllable-based measures and is used in education, publishing, and automated content analysis. It is one of the six formulas in Harvard CS50 readability assignments.

Why Use Coleman-Liau Index?

  • Deterministic results with no syllable-counting ambiguity
  • Maps directly to U.S. grade levels
  • Extremely fast computation for real-time analysis
  • Complements syllable-based formulas
  • Ideal for automated content pipelines

Common Use Cases

Large-Scale Analysis

Analyze thousands of documents quickly with reliable character counting.

Educational Assessment

Match materials to grade levels with a formula designed for this purpose.

Automated Pipelines

Integrate into CMS for automated readability gates.

Cross-Formula Validation

Use alongside Flesch-Kincaid for multi-perspective assessment.

Technical Guide

L = (letters/words)*100, S = (sentences/words)*100. Letters are alphabetic characters only. The positive coefficient on L means longer words increase grade level. More sentences per 100 words (shorter sentences) decrease it. A CLI of 6 suits newspapers, 14+ indicates college-level material. The tool clamps minimum to grade 1.

Tips & Best Practices

  • 1
    CLI of 6-8 is ideal for web content
  • 2
    Reduce average word length to lower the score
  • 3
    More stable on technical texts than syllable-based formulas
  • 4
    Pair with Flesch-Kincaid for balanced assessment

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Frequently Asked Questions

Q How is it different from Flesch-Kincaid?
Uses character counts instead of syllable counts, making it deterministic and unambiguous.
Q What is a good score?
6-8 for general audiences. Below 6 is very easy, above 12 is college-level.
Q Does it work for non-English?
Calibrated for English. Coefficients may not produce meaningful grades for other languages.
Q Can scores be negative?
Theoretically yes for very simple text. The tool clamps to grade 1 minimum.
Q Why characters instead of syllables?
Character counting is unambiguous. Syllable counting relies on heuristics with occasional errors.

About This Tool

Coleman-Liau Index is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.