Last updated: March 2026
The Flesch-Kincaid Readability Formula Explained
The Flesch-Kincaid readability tests are the most widely used readability formulas in the world. They power the readability statistics in Microsoft Word, are required by the U.S. Department of Defense for technical manuals, and are the standard benchmark for plain-language compliance in healthcare, insurance, and government communications.
There are actually two separate formulas. The Flesch Reading Ease score rates text on a 0–100 scale where higher numbers mean easier reading. The formula is: 206.835 − 1.015 × (total words / total sentences) − 84.6 × (total syllables / total words). A score of 60–70 corresponds to plain English that an average adult can read comfortably.
The Flesch-Kincaid Grade Level converts the same inputs into a U.S. school grade level. The formula is: 0.39 × (words / sentences) + 11.8 × (syllables / words) − 15.59. A result of 8.0 means the text should be understandable by an 8th grader. This grade-level output makes it intuitive to compare against audience education levels.
Both formulas rely on two measurable properties of text: average sentence length and average syllables per word. Longer sentences increase cognitive load because readers must hold more information in working memory before reaching a full stop. Words with more syllables tend to be less common and more abstract, requiring more effort to decode and understand.
To improve your Flesch-Kincaid scores, focus on two things. First, break long sentences into shorter ones — aim for 15–20 words per sentence on average. Second, replace multi-syllable words with shorter synonyms where meaning allows. "Use" instead of "utilize," "help" instead of "facilitate," "start" instead of "commence." These simple substitutions can drop your grade level by two or more points.
Frequently Asked Questions
What is the Flesch-Kincaid Grade Level?
The Flesch-Kincaid Grade Level formula converts text complexity into a U.S. school grade level. A score of 8.0 means an 8th grader can understand the text. The formula is: 0.39 * (words/sentences) + 11.8 * (syllables/words) - 15.59. Lower scores mean simpler text.
What is the Flesch Reading Ease score?
The Flesch Reading Ease score rates text on a 0-100 scale, where higher scores mean easier reading. The formula is: 206.835 - 1.015 * (words/sentences) - 84.6 * (syllables/words). A score of 60-70 is considered standard plain English.
Who created the Flesch-Kincaid formula?
Rudolf Flesch developed the original Reading Ease formula in 1948. J. Peter Kincaid later adapted it into the Grade Level formula in 1975 for the U.S. Navy to assess the readability of technical manuals. Both formulas are now widely used in education, government, and business.
What Flesch-Kincaid score should I aim for?
For general web content, aim for grade 6-8. Marketing and consumer content works best at grade 6-7. Health information should be grade 6 or lower. Business reports can be grade 8-10. Academic and technical writing is typically grade 12+. The best target depends on your specific audience.
How do Flesch-Kincaid and Gunning Fog compare?
Both measure readability but differ in approach. Flesch-Kincaid counts total syllables per word. Gunning Fog counts 'complex words' (3+ syllables) as a percentage. Fog tends to give slightly higher grade levels because it treats any 3-syllable word as complex, even common ones like 'important' or 'beautiful'.
Can I use Flesch-Kincaid for non-English text?
The original formula was designed for English. Syllable counting rules and the calibration constants are based on English word patterns. Modified versions exist for some other languages (German, Spanish, Dutch), but they use different coefficients. This tool is calibrated for English text.