Readability Scoring

The most widely implemented readability metric in content management systems and word processors. It correlates average sentence length and average syllables per word to a U.S. school grade level.

• Formula: 0.39 × (words/sentences) + 11.8 × (syllables/words) - 15.59
• Output: A score from 0 to 18 representing grade level
• Use case: Military documentation standards (MIL-STD-1472) require a score of 9th grade or below
• Limitation: Penalizes all long words equally, including familiar terms like "university"

The precursor to Flesch-Kincaid, this formula produces a 0-100 scale where higher scores indicate easier readability. It uses the same core variables but weights them differently.

• Formula: 206.835 - 1.015 × (words/sentences) - 84.6 × (syllables/words)
• Score interpretation: 90-100 (Very Easy, 5th grade) to 0-30 (Very Difficult, college graduate)
• Industry standard: Insurance policies often target a score of 45 or higher
• Key insight: The inverse relationship with grade level formulas makes it useful for A/B testing content variants

Designed specifically for business writing, this formula estimates the years of formal education needed to understand a text on first reading. It introduces the concept of complex words—polysyllabic words with three or more syllables.

• Formula: 0.4 × [(words/sentences) + 100 × (complex words/words)]
• Target range: Scores of 7-8 for general audience; below 12 for most professional writing
• Distinction: Excludes proper nouns, compound words, and common suffixes from complex word count
• Criticism: The arbitrary three-syllable threshold can misclassify simple compound words

The Simple Measure of Gobbledygook is widely used in healthcare to ensure patient-facing materials are accessible. Unlike other formulas, it uses a sampling method rather than analyzing the full text.

• Method: Count polysyllabic words (3+ syllables) in 30 sentences (10 from beginning, middle, and end)
• Formula: 1.043 × √(polysyllabic count × (30/sentences sampled)) + 3.1291
• Clinical relevance: Required by many Institutional Review Boards for informed consent documents
• Accuracy: Research shows SMOG correlates more strongly with comprehension tests than Flesch-Kincaid

Unique among readability formulas because it relies on character counts rather than syllable counts, making it computationally simpler and language-agnostic for alphabet-based languages.

• Formula: 0.0588 × L - 0.296 × S - 15.8 (where L = avg letters per 100 words, S = avg sentences per 100 words)
• Advantage: No syllable dictionary required; purely statistical from character analysis
• Use case: Automated content scoring pipelines where syllable parsing is unreliable
• Trade-off: Less accurate for languages with irregular orthography compared to syllable-based methods

Developed for military technical manual assessment, ARI uses character count per word and word count per sentence to output a grade level. It was designed for real-time typing assessment.

• Formula: 4.71 × (characters/words) + 0.5 × (words/sentences) - 21.43
• Output: Correlates directly to U.S. grade levels, with scores above 14 indicating college-level difficulty
• Efficiency: Requires only character counting, making it ideal for programmatic content infrastructure pipelines
• Validation: Originally tested against 330 military training manuals with high correlation to human comprehension scores