Grade Level Scores

Grade level metrics estimate the US school grade level required to understand the text.

Metrics Comparison

Metric	Focus	Best For
Flesch-Kincaid	Sentence length, syllables	General use
ARI	Characters per word	Technical content
Gunning Fog	Complex words	Business writing
SMOG	Polysyllables	Healthcare/education
Coleman-Liau	Character counts	Academic assessment

Flesch-Kincaid Grade Level

The most common grade-level metric.

Formula:

0.39 × (words / sentences) + 11.8 × (syllables / words) - 15.59

ARI (Automated Readability Index)

Uses characters instead of syllables, making it more consistent for technical content.

Formula:

4.71 × (characters / words) + 0.5 × (words / sentences) - 21.43

Gunning Fog Index

Focuses on "complex words" (3+ syllables, excluding common suffixes).

Formula:

0.4 × ((words / sentences) + 100 × (complex words / words))

Which to Use?

• Technical documentation: Use ARI or Flesch-Kincaid
• Business content: Use Gunning Fog
• Healthcare/education: Use SMOG
• General purpose: Use Flesch-Kincaid as primary