Readability Scores Explained: Flesch-Kincaid, Gunning Fog & SMOG

Readability scoring formulas measure how easily a human reader can understand written text. Readability scores are useful signals for comparing how easy text may be to read; they do not guarantee engagement or search rankings.

The Core Readability Formulas

1. Flesch Reading Ease (FRE)

Scored on a scale from 0 to 100:

• 90 – 100: Very Easy (5th grade level). Clean, simple conversational copy.
• 60 – 70: Standard / Plain English (8th – 9th grade). Ideal for web content and blog posts.
• 30 – 50: Difficult (College level). Academic journals and technical documentation.
• 0 – 30: Very Difficult (University graduate level). Legal contracts and scientific papers.

2. Flesch-Kincaid Grade Level

Translates reading ease directly into U.S. school grade levels. An FK score of 8.0 means an 8th grader can comfortably understand the text.

3. Gunning Fog Index

Estimates the years of formal education required to comprehend text on first reading by analyzing the percentage of complex words (words containing 3 or more syllables).

Actionable Tips to Improve Readability

1. Keep average sentence length under 20 words.
2. Replace polysyllabic jargon with crisp, direct synonyms using our Online Thesaurus.
3. Eliminate passive voice using our Grammar & Style Checker.
4. Test your draft in the Advanced Readability Checker.