READABILITY
Readability Formulas Explained: Flesch, Fog, SMOG and More
Understand common readability formulas, what their scores mean and why a formula should never be treated as the whole quality of a document.
Readability formulas turn measurable features such as sentence length and word complexity into an estimate. They are useful for comparing drafts, but they are not a complete measure of writing quality.
Flesch Reading Ease and Flesch-Kincaid
Flesch Reading Ease uses sentence length and syllables per word to estimate difficulty; higher scores generally indicate easier English prose. Flesch-Kincaid converts similar signals into an estimated U.S. school grade level.
Gunning Fog and SMOG
Gunning Fog incorporates sentence length and complex words. SMOG estimates the years of education needed to understand a passage using polysyllabic-word counts. Both are useful as comparative signals for English text.
Coleman-Liau and ARI
Coleman-Liau relies more heavily on characters and sentence structure, while the Automated Readability Index uses character-based word complexity and sentence length. Different formulas can disagree because they measure different proxies.
Use scores responsibly
Readability formulas are primarily calibrated for English and should not be treated as universal linguistic measures. For specialized audiences, accuracy, terminology and context can matter more than achieving a particular numeric score.
Frequently asked questions
What is a good readability score?
It depends on the audience and document type. A score is most useful when compared with the intended reading level and with earlier drafts.
Does readability equal quality?
No. Readability is one dimension of writing quality.