Ever feel like you’re writing into a void? You’ve poured hours into crafting your docs but somehow something just doesn’t click with users? Well, maybe this something is a problem with readability.
Meet the Coleman-Liau Index. Let’s take a look into this readability compass and see how it can sharpen your content’s impact.
What Is the Coleman-Liau Index?
The Coleman-Liau Index is a readability formula designed to estimate the grade level required to understand a text. Unlike other formulas (e.g., Flesch-Kincaid), it relies on characters per word and sentences per word instead of syllable counts, making it easier for computer programs to calculate.
Developed by linguists Meri Coleman and T. L. Liau in the 1970s, it’s still widely used in education, publishing, and content creation to ensure texts match the reading level of their audience.
Key advantages:
- No need to count syllables—use characters and sentences.
- Works well for non-English texts.
- Provides a quite accurate measure of reading difficulty.
Who Uses the Coleman-Liau Index?
- Technical writers simplifying complex information for broader audiences.
- Educators assessing textbook difficulty for schools.
- Researchers analyzing literacy trends.
- Content creators tailoring blogs or articles to specific grade levels.
Coleman-Liau Formula
For reliable results, analyze texts with at least 300 words. Shorter passages may produce less consistent scores as a single complex sentence or word can disproportionately affect the outcome.
Coleman-Liau Index (CLI) =
0.0588 x (Characters per 100 words) – 0.296 x (Sentences per 100 words) – 15.8
How to Calculate CLI Manually
Though we’d recommend using a tool, here’s a step-by-step guide to manually calculate the Coleman-Liau Index (CLI) for any text.
In case you need to better understand why your content scores a certain grade level, spot-check automated tools, or fine-tune readability for niche audiences.
Step 1.
Choose a sample (at least 100 words for accuracy). For shorter texts, extrapolate results proportionally.
Step 2.
- Count the total number of characters in your text (including letters, numbers, punctuation, and spaces).
- Count the total number of words.
- Count the total number of sentences.
Note: Abbreviations (e.g., “Mr.” or “etc.”) count as part of the sentence they’re in.
Step 3.
- Calculate characters per 100 words (A):
A=(Total Characters ÷ Total Words) × 100
- Calculate sentences per 100 words (B):
B=(Total Sentences ÷ Total Words) × 100
- Multiply A by 0.0588
- Multiply B by 0.296
- Subtract B*0.296 from A*0.0588
- Subtract 15.8 from the result
For example, if you have a text with:
- 500 characters
- 100 words
- 5 sentences
The calculation would be:
- Characters per 100 words (A) = (500 ÷ 100) × 100 = 500
- Sentences per 100 words (B) = (5 ÷ 100) × 100 = 5
- CLI = (0.0588 × A) – (0.296 × B) – 15.8
CLI= (0.0588 × 500) – (0.296 × 5) – 15.8
- CLI = 29.4 – 1.48 – 15.8
- CLI = 12.12
Step 4. Interpret your score.
What Does Your Score Mean?
CLI score corresponds to the U.S. school grade level needed to comprehend the text.
| Coleman-Liau Score | Reading Level |
| 5–6 | 5th–6th grade (Elementary) |
| 7–8 | 7th–8th grade (Middle School) |
| 9–10 | High School |
| 11–12 | College Prep |
| 13+ | Professional/Technical |
Note: Aim for a score matching your audience (e.g., blogs target 7th–8th grade).
How to Improve Your Coleman-Liau Score
To lower the grade level, simplify text.
- Shorten sentences. Use periods instead of commas.
- Use simpler words. Replace complex terms (e.g., “utilize” → “use”).
- Avoid jargon. Ensure language is accessible to non-experts.
- Break up paragraphs. Improve flow and reduce reading fatigue.
And you don’t have to do it manually. The readability calculators (e.g., WebFX Coleman-Liau Tool) or grammar checkers (e.g., Grammarly) might be of great help.
Coleman-Liau vs. Other Readability Formulas
Readability formulas assess text using different criteria. The table below compares the Coleman-Liau Index with other popular methods, helping you choose the best tool for your needs.
| Formula | Focus | Best For |
| Coleman-Liau | Characters, sentences | Computer analysis, non-English |
| Flesch-Kincaid | Syllables, sentences | General readability |
| Gunning Fog | Complex words, sentences | Technical documents |
| ARI | Characters, words | Academic texts |
FAQs About the Coleman-Liau Index
Q: How accurate is the Coleman-Liau Index?
A: Studies have shown the Coleman-Liau Index to be reasonably accurate for English texts. However, like all readability formulas, it provides an estimate rather than a definitive assessment. For best results, combine it with other readability metrics and actual reader feedback.
Q: How does Coleman-Liau differ from Flesch-Kincaid?
A: Coleman-Liau uses characters, not syllables, making it better for computer programs and multilingual texts.
Q: Can I use it for non-English content?
A: Yes! It’s rather effective for languages where syllable counts are tricky.
Q: How many characters should I count? Do spaces and punctuation count?
A: Count all characters including letters, numbers, punctuation marks, and spaces. This total character count is what the formula requires for accurate results.
Q: Why is the constant 15.8 used in the formula?
A: The constant 15.8 was empirically determined by Coleman and Liau through statistical analysis of texts with known difficulty levels. It calibrates the formula to align with U.S. grade level standards.
Conclusion
Mastering the Coleman-Liau Index isn’t just about hitting a grade-level target—it’s about creating technical documentation that’s both precise and accessible. By focusing on clarity, you ensure your content reaches the audience, while we at ClickHelp ensure your technical documentation is safely stored and easily accessed.
Try our free trial or book a demo to see for yourself.
Good luck with your technical writing!
ClickHelp Team
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