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Coleman-Liau Index Calculator

Compute the Coleman-Liau readability index from letters and sentences per 100 words — no syllable guessing. Free, instant and fully in-browser.

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Coleman–Liau Index
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Letters
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Words
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Sentences
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L (letters / 100 words)
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S (sentences / 100 words)

What is the Coleman-Liau Index Calculator?

The Coleman–Liau Index estimates the US grade level of your text using characters instead of syllables: CLI = 0.

  • Exact character-based formula — no syllable estimation error
  • Shows L and S intermediate values, not just the final index
  • Approximate US grade-level interpretation
  • Letter, word and sentence counts included
  • 100% offline — your text never leaves the browser

How to use the Coleman-Liau Index Calculator

  1. 1

    Paste your text into the input box.

  2. 2

    Read the Coleman–Liau Index and its approximate grade band.

  3. 3

    Check L (letters per 100 words) and S (sentences per 100 words) to see what drives the score.

  4. 4

    Edit your text and watch the index update as you type.

About the Coleman-Liau Index Calculator

The Coleman–Liau Index estimates the US grade level of your text using characters instead of syllables: CLI = 0.0588 × L − 0.296 × S − 15.8, where L is letters per 100 words and S is sentences per 100 words. Paste your text and this calculator shows the index, both intermediate values and the underlying counts.

Because letters can be counted exactly while syllables must be estimated, Coleman–Liau has no syllable-estimation error — a property that made it practical for machine scoring from the start. It is a useful cross-check next to syllable-based formulas like Flesch–Kincaid, Gunning Fog and SMOG: when they disagree, CLI tells you whether long words or long sentences are responsible.

The analysis runs 100% locally in your browser. Nothing you paste is uploaded or stored, and the calculator keeps working offline.

Frequently asked questions

How is the Coleman-Liau Index calculated?

CLI = 0.0588 × L − 0.296 × S − 15.8. L is the average number of letters per 100 words and S the average number of sentences per 100 words. A CLI of 10 means roughly tenth-grade reading level.

Why use letters instead of syllables?

Letters can be counted with zero error, while syllable counting always relies on pronunciation rules. Coleman and Liau designed the index in 1975 so computers could score text reliably without a pronunciation dictionary — the same reason it remains a good automated cross-check today.

Is Coleman-Liau more accurate than Flesch-Kincaid?

Neither is universally better — they weight different signals. CLI reacts to long words measured in letters, Flesch–Kincaid to syllables and sentence length. On typical prose they land within a grade or two of each other; big gaps usually mean your words are long in letters but not in syllables, or vice versa.

What is a good CLI score for web content?

General web copy usually aims for grade 7–9. Above 12, casual readers start skimming or bouncing. Legal, medical and academic material naturally scores higher — compare against your genre, not a universal target.

Does this tool upload my text?

No. Everything is computed in your browser with JavaScript, so drafts and confidential text stay on your device.

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