When Should I Use Readability Formulas and When Should I Not?

Readability formulas are tools that analyze the readability of text, usually by calculating sentence length, word length, and syllables. Most formulas output a score that matches a grade or reading level. This number, along with other stats, can help writers and non-writers craft content that readers can comprehend. You can use these formulas to score most types of texts, but not all.

(The Flesch-Kincaid Formula outputs a score that matches a U.S. grade level. This tells you the text is appropriate for 5th grade students or any readers with a 5th grade or higher education.)

When to Use Readability Formulas

✓  Educational Content.  Readability formulas can help teachers match textbooks and educational content to the reading level of students.

“Teachers using readability data reported a 25% improvement in overall student comprehension and engagement,” according to Thomas G. Gunning, author of Creating Literacy Instruction for All Students.

For example, a 5th-grade teacher might use the Flesch-Kincaid Formula to determine if she can use a new science textbook for her class.

✓  Health Communications.  Readability formulas can help create easy-to-understand materials for the general population. Patient information leaflets, consent forms, and public health notices must be accessible to people with varying literacy levels.

The Centers for Disease Control and Prevention (CDC) suggests health information be written two levels below the population’s average grade reading level—a 6th-grade reading level. For individuals over 65, the agency suggests an even lower reading level​.

✓  Legal Documents.  Policies, laws, and regulations need to be readable to non-specialists. Readability formulas can help simplify legalese without oversimplifying the content.

The U.S. Department of Health & Human Services (HHS) emphasizes that plain writing is mandated by law and counters the myth that content must be “dumbed down” for plain language. Instead, the focus is on clear communication—accessible to the audience.

✓  Publishing Industry.  Editors and publishers use readability scores to find out if a text is appropriate for their target audience. This is especially true for children’s stories for English language learners. “Using readability formulas for English language learners can improve text comprehension outcomes by up to 30%,” according to E. H. Hiebert, author of Text Complexity and English Language Learners.

✓  News Articles.  In constantly-changing environments, journalists and reporters gather and translate complex information and write their articles that cater to the general public. Readability formulas help these professionals use simple language, with straightforward sentences and common, high-frequency words. This style is important when they report on critical updates affecting how communities react and stay safe.

The Associated Press Stylebook advises journalists to use short words and sentences to improve readability, as this style resonates better with a wider audience.

✓  Web Content.  With the vast range of literacy levels among Internet users, web content creators can use readability formulas to ensure their information is accessible to a wider audience.

According to the World Wide Web Consortium (W3C), “Content should be readable and understandable by a range of users, and readability formulas are an effective way to measure this.“

✓  User Manuals/Instructions.  For products that reach a diverse consumer audience, customers need to follow installation instructions despite lacking technical know-how. Readability formulas can help technical writers craft clear how-to instructions.

“Over 60% of product-related accidents are due to unclear or poorly written instructions. Readability assessments are key to mitigating these risks,” according the International Journal of Industrial Ergonomics.

✓  Business Communications.  In the corporate world, clarity is paramount. Whether it’s memos, reports, or emails, readability formulas can help professionals communicate more effectively with their colleagues.

The Corporate Leadership Council reports that “Companies that prioritize clear and readable communication experience a 30% increase in employee engagement and a 25% improvement in decision-making processes.”

✓  Advertising Copy.  Readability formulas help copywriters craft messages that capture the attention of potential customers. “Messages that are simple and easy to understand tend to stick better with audiences; readability plays a key role in making sure that even complex ideas are presented in a way that attracts attention,” according to Chip Heath, author of Made to Stick: Why Some Ideas Survive and Others Die.

✓  Social Media.  With the rapid scrolling culture of social media, posts with better readability are more likely to engage a broader audience. These formulas can guide content creators in crafting digestible messages. “Clear and accessible messages are more likely to influence behavior and opinions in the online social sphere,” according to The American Psychological Association (APA).

✓  Grant Writing.  When seeking funding, it’s crucial the grant proposal is clear to all reviewers. Readability formulas can help writers refine the language to express key points effectively. According to Jeremy T. Miner, author of Proposal Planning & Writing, “Proposals that use readability formulas to simplify language had an 18% higher rate of being shortlisted for funding.”

✓  Public Speaking.  Speakers can use readability formulas to ensure their audience can understand their message easily. By running their text through multiple formulas, speakers can test if their language is accessible across different standards.

When Not to Rely on Readability Formulas

✗  Nuanced or Creative Writing.  Literature, poetry, and certain forms of creative non-fiction often play with language in ways that are intentionally complex or challenging. Readability formulas do not account for stylistic choices or the artistic merit of text.

✗  Technical or Specialist Texts.   Academic papers, technical manuals, and industry-specific reports are meant for specialized audiences who understand jargon and complex ideas. Not all formulas will accurately score the appropriateness of these texts. For advanced and technical texts, users can use the FORCAST Formula.

✗  Cultural Sensitivity.    Because these formulas are based on syntactic and lexical measures, they do not consider cultural references, idioms, or regional language variations—these can be important in multicultural or multilingual contexts.

✗  Audience Engagement.   Sometimes the goal of a text is to engage readers more deeply with the content. A higher readability score may not reflect the text’s engagement.

✗  Marketing Materials.   These often aim for impact, brevity, and memorability rather than adherence to readability standards. Slogans, for instance, may not conform to readability standards but are effective in their context.

✗  Cultural Literature/Folklore.   These texts are often rich in cultural expressions and linguistic nuances that readability formulas cannot account for. The educational value and cultural significance lie beyond the scope of what readability scores can measure.

✗  Satire and Irony.   Satirical writing or irony often hinges on language and the double meanings that readability formulas would likely misinterpret as complexity rather than stylistic devices.

✗  Poetry/Abstract Writing.   Poetry and certain forms of abstract prose deliberately flout conventional syntax and vocabulary to evoke emotions or sensory effects, which readability formulas are not equipped to appreciate.

✗  Dialogue Texts.   Plays, scripts, and novels that feature a lot of dialogue may mislead readability scores because the spoken language is often more colloquial and fragmented than formal prose.

✗  Persuasive Texts.   Political speeches, opinion pieces, and advocacy materials are crafted to persuade and may use rhetorical devices that are not quantifiable by readability metrics but are central to the text’s effectiveness.

✗  Transcribed Speeches/Interviews.   The informal and spontaneous nature of spoken language does not always translate into high readability scores, despite being easily understood in its spoken form.

✗  Slang and Jargon.   Texts that appeal to specific groups or subcultures through slang, technical jargon, or insider language may score less readable, yet they communicate effectively within their target group.

✗  Experimental Writing.   Some authors may experiment with language and structure to challenge readers or to convey complex themes and ideas that readability formulas are not designed to capture.

✗  Historical Texts.   The language in historical documents often contains archaic vocabulary and syntax that readability formulas may score as complex, even though such texts are crucial for understanding history and culture.

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