Why Coleman-Liau Works Where Flesch-Kincaid Fails: A Syllable-Free Alternative

Readability formulas feel precise—they spit out a number and promise you a grade level. But behind that number lies a measurement choice that can shift your writing's perceived complexity by 1.3 grade levels.

The culprit: syllables.

Flesch-Kincaid Grade Level, the standard formula in Microsoft Word and most LMS platforms, counts syllables. But English syllables are ambiguous. Is "every" two syllables or three? Is "business" two or three? Editors disagree. Automated systems guess. And that guessing breaks down fastest when you need it most—in medical writing, compliance, and content for second-language readers.

Coleman-Liau Index sidesteps the problem entirely. It counts characters instead.

This matters more than it sounds. Character counts are deterministic. There's no judgment call. A 5-letter word is always 5 letters. That shift from syllable-counting to character-counting produces a formula that's more objective, faster to automate, and increasingly preferred by accessibility tools and non-English writing systems.

How Flesch-Kincaid Counts

Flesch-Kincaid Grade Level uses three variables:

• Words (W)
• Sentences (S)
• Syllables (SY)

The formula:

Grade = (0.39 × W/S) + (11.8 × SY/W) − 15.59

Read this sentence from a SaaS onboarding page:

"Our platform automates your customer data aggregation workflow."

Flesch-Kincaid count:

• Words: 8
• Sentences: 1
• Syllables: Let's count. "Our" (1) "plat-form" (2) "au-to-mates" (3) "your" (1) "cus-to-mer" (3) "da-ta" (2) "ag-gre-ga-tion" (4) "work-flow" (2) = 18 syllables

Grade = (0.39 × 8/1) + (11.8 × 18/8) − 15.59 = 3.12 + 26.55 − 15.59 = 14.08 (college senior)

But watch what happens when you count "aggregation." Some counters say "ag-gre-ga-tion" (4). Others say "a-gre-gay-shun" (3). Suddenly your sentence drops to 17 syllables, and the grade becomes 13.5. Change one word's syllable count by one and your grade level shifts.

How Coleman-Liau Counts

Coleman-Liau Index replaces syllables with characters. The formula:

Grade = (0.0588 × C) − (0.296 × S) − 15.8

Where:

• C = characters (letters, not including spaces or punctuation)
• S = sentences

Same sentence: "Our platform automates your customer data aggregation workflow."

Coleman-Liau count:

• Characters: o-u-r-p-l-a-t-f-o-r-m-a-u-t-o-m-a-t-e-s-y-o-u-r-c-u-s-t-o-m-e-r-d-a-t-a-a-g-g-r-e-g-a-t-i-o-n-w-o-r-k-f-l-o-w = 48 characters
• Sentences: 1

Grade = (0.0588 × 48) − (0.296 × 1) − 15.8 = 2.82 − 0.296 − 15.8 = −13.276, clipped to 0 (kindergarten, or "too easy to measure")

That's too low—our sentence is clearly not kindergarten-level. The issue: Coleman-Liau was calibrated on elementary-school texts with short words. On longer, technical vocabulary, it undercounts.

But here's the real test. Let's expand the sentence slightly:

"Our platform automates customer data aggregation and enrichment workflows for SaaS teams."

Flesch-Kincaid:

• Words: 13
• Sentences: 1
• Syllables: 3+2+3+2+3+2+4+3+2+1+1+1+2 = 30 syllables (wait, did you count "enrichment" as 2 or 3? Most counters say 3: en-rich-ment. Some say 2: en-richment. See the problem?)

With 30 syllables: Grade = (0.39 × 13) + (11.8 × 30/13) − 15.59 = 5.07 + 27.23 − 15.59 = 16.71

Coleman-Liau:

• Characters: 81
• Sentences: 1

Grade = (0.0588 × 81) − (0.296 × 1) − 15.8 = 4.76 − 0.30 − 15.8 = −11.34, clipped to 0

Coleman-Liau still bottoms out, but Flesch-Kincaid swings wildly depending on how you count "enrichment." That variability is the vulnerability.

Where Character Counting Wins

Automated systems and APIs: When you're scoring readability in real time—in a CMS, accessibility checker, or AI-powered editor—you can't afford to make judgment calls. Syllable counting requires linguistic rules (Is the final 'e' silent? Does 'tion' add one syllable?). Character counting is instantaneous.

Grammarly, Hemingway Editor, and Microsoft's built-in readability checker have all shifted toward character-based or hybrid metrics for this reason. Grammarly's internal readability model uses character count as a foundational layer precisely because it's reproducible.

Non-English and multilingual content: If you're writing for ESL audiences or supporting content in multiple languages, character-based metrics become critical. Syllable counting is language-specific. English syllable rules don't apply to German compound words or French liaison. Character count is universal. A Finnish L2 English reader benefits from knowing that a 60-character-average sentence is harder than a 40-character one, regardless of how linguists divide syllables.

Medical and compliance writing: In healthcare and legal tech, consistency matters more than accuracy within 0.5 grades. Compliance reviewers want to know: Does this consent form stay under grade 8? Is this patient-education page accessible to most adults? A character-based formula, while less granular, gives you a repeatable standard. Two reviewers using Coleman-Liau will always get the same score for the same text. Two reviewers using Flesch-Kincaid might not.

Real Example: A B2B SaaS Paragraph

Here's a typical SaaS feature description:

"Activate advanced segmentation capabilities to create targeted cohorts from behavioral, demographic, and transaction attributes. Our rules engine supports nested conditions, exclusion lists, and frequency capping—enabling sophisticated audience strategies without coding."

Flesch-Kincaid breakdown:

• Words: 27
• Sentences: 2
• Syllables (conservative count): 3+1+3+4+2+2+2+2+3+2+2+2+3+2+1+2+3+3+2+3+1+2+2+2+1+1+2 = 59

Grade = (0.39 × 27/2) + (11.8 × 59/27) − 15.59 = 5.27 + 25.75 − 15.59 = 15.43

(But syllable disagreement could shift this ±1 grade easily.)

Coleman-Liau breakdown:

• Characters: 281
• Sentences: 2

Grade = (0.0588 × 281) − (0.296 × 2) − 15.8 = 16.52 − 0.59 − 15.8 = 0.13, clipped to 0

Again, Coleman-Liau underperforms on technical vocabulary. But notice: it doesn't fluctuate based on syllable interpretation. You'd get the same score tomorrow, and so would every other tool using the same formula.

Which Formula Should You Use?

Use Flesch-Kincaid if:

• You're writing for school districts, educational publishers, or institutions that mandate it.
• Your audience is general English-speaking adults and you value the familiarity of the metric.
• You're not automating the score and can verify syllable counts manually.

Use Coleman-Liau if:

• You're building automated readability checks into software or a CMS.
• Your content targets non-native English speakers.
• You need reproducible scores across multiple reviewers or systems.
• You're writing medical, legal, or compliance content where consistency trumps granularity.

The Hybrid Approach

Leading grammar-checking tools don't pick one. Hemingway Editor reports multiple metrics. Grammarly uses a proprietary model that blends character density, word frequency, and sentence structure. For serious writers, the takeaway is:

Don't rely on a single formula. If Flesch-Kincaid says grade 10 and Coleman-Liau says grade 0, something's wrong with your vocabulary or your measurement. Rewrite for clarity—the word choice that scores well on both metrics is almost always the clearer choice.

The shift from syllable-counting to character-counting reflects a larger evolution in readability science: from linguistic precision (which varies) to computational reproducibility (which doesn't). Syllable counting is more granular in theory. Character counting is more reliable in practice.

For writers and editors managing readability across teams, across time, or across systems, that reliability is worth the trade-off.