Flesch-Kincaid Readability: How to Write Content Anyone Can Read

Most writers know what they want to say. Fewer know whether what they wrote is actually easy to read. The gap between clarity in your head and clarity on the page is where readers get lost, stop reading, and leave.

The Flesch-Kincaid readability formulas are the most widely used tools for measuring text complexity. They are used by educators, content marketers, government agencies, medical writers, and software developers to ensure that written content reaches its intended audience. Here is how they work and what you can do with the scores.

Who Created the Flesch-Kincaid Formulas?

Rudolf Flesch was an Austrian-born American author and readability expert who created the original Flesch Reading Ease formula in 1948. J. Peter Kincaid, a researcher at the US Navy, adapted the formula in 1975 to produce a grade-level equivalent. Together, these two formulas are known as the Flesch-Kincaid tests and are the standard readability measures in most writing tools today.

The US Department of Defense required that all military documents meet specific readability standards based on these formulas, which drove their widespread adoption.

Flesch Reading Ease Score

The Flesch Reading Ease score is a number between 0 and 100. Higher scores indicate text that is easier to read. Lower scores indicate more complex, difficult text.

The Formula

Reading Ease = 206.835 - (1.015 x average words per sentence) - (84.6 x average syllables per word)

Score Interpretation

The Wall Street Journal typically scores around 60-65. Reader's Digest scores around 65. Academic journals often score below 30. For most web content, a score of 60-70 is a good target.

Flesch-Kincaid Grade Level

The Flesch-Kincaid Grade Level converts the reading ease measurement into a US school grade level equivalent. A score of 8.0 means the text is appropriate for an 8th-grade reading level.

The Formula

Grade Level = (0.39 x average words per sentence) + (11.8 x average syllables per word) - 15.59

What Grade Level to Target

• General blog content: Grade 6-8
• News articles: Grade 8-10
• Business writing: Grade 8-10
• Legal documents (required by some US states): Grade 6-8
• Medical patient education materials: Grade 6-8
• Academic papers: Grade 12-16+

Note that targeting a lower grade level does not mean "writing for children." It means writing clearly and directly. The same information can be expressed at a grade 7 level or a grade 14 level — the grade 7 version is simply more accessible to a broader audience.

What Drives Readability Scores

Two factors dominate both Flesch-Kincaid formulas:

1. Sentence Length

Long sentences are harder to parse. The working memory required to track a sentence increases with each clause added. A sentence with three dependent clauses, two parenthetical asides, and multiple referenced concepts requires the reader to hold all of those threads simultaneously until the sentence ends.

Compare: "The long complex sentence above required significant working memory to parse because of its multiple nested clauses" versus "Long sentences are hard to read."

Both say something similar. The second is faster and clearer.

Target for most content: 15-20 words per sentence on average.

2. Syllable Count Per Word

Multi-syllable words require more cognitive processing than short words. "Utilize" has three syllables; "use" has one. "Demonstrate" has four syllables; "show" has one. In most cases, the shorter word is equally precise and significantly easier to read.

This does not mean avoiding technical terminology when it is necessary and precise. It means not using long words when short ones do the job just as well.

Other Readability Formulas

The Flesch-Kincaid tests are the most widely used but not the only readability measures:

Gunning Fog Index: Focuses on the percentage of "hard words" (three or more syllables) in the text. A score of 12 means 12th-grade reading level.

SMOG Grading: Particularly popular in healthcare writing. Estimates the years of education needed to understand a piece of writing.

Coleman-Liau Index: Uses characters per word and sentences per paragraph rather than syllables, which makes it easy to compute programmatically.

Automated Readability Index (ARI): Also uses characters and words rather than syllables.

Different formulas agree most of the time, but they can diverge on specific texts. Most readability checkers show multiple scores simultaneously so you get a more complete picture.

Practical Tips for Improving Readability

Break up long sentences. Any sentence over 30 words should be reviewed and probably split. Look for conjunctions (and, but, because, which) as natural split points.

Use short, common words. Before using a long word, ask whether a shorter synonym works equally well. "End" vs "terminate," "buy" vs "purchase," "help" vs "facilitate."

Write in active voice. Passive voice adds words and obscures agency. "The report was written by the team" becomes "The team wrote the report."

Vary sentence length deliberately. A wall of identically short sentences feels choppy. A wall of long sentences feels exhausting. Mix them, but let the average stay low.

Use headings and bullet points. These are not captured by readability formulas but dramatically affect how easy content is to navigate and scan.

Cut unnecessary qualifiers. Words like "very," "really," "quite," "essentially," and "basically" rarely add meaning and always add length.

Readability in Specific Contexts

SEO content: Google's systems evaluate content quality partly through user engagement signals. Easier-to-read content tends to keep readers on page longer and reduce bounce rates, which are positive signals.

Healthcare: US federal guidelines recommend patient education materials at a grade 6-8 reading level. Research consistently shows that lower-literacy patients have worse health outcomes when materials are written above their comprehension level.

Legal and government: Plain language requirements in the US, UK, and EU mandate that public-facing government documents be written clearly. The US Plain Writing Act (2010) requires federal agencies to use plain language.

Marketing and advertising: Direct response copy has historically performed better at lower reading levels. Short sentences and simple words convert better than complex prose.

Check Your Own Writing

Pasting your text into a readability checker shows you the scores before you publish and highlights which sentences and words are pulling your readability down.