Dale-Chall Readability Formula: How It Works and When to Use It

In presenting new information, clarity is more essential than ever. Whether you’re addressing students, experts, or a general audience, your message must be easy to understand. That’s where readability formulas come in. One of the most established, well-researched, and widely used tools is the Dale-Chall Readability Formula. Known for its precision and application in education, this formula helps writers assess how easily their content can be understood by readers at various grade levels.

In this article, we’ll explore what the Dale-Chall Readability Score is, how it was developed, how it works, when to use it, and how to interpret your results.

What Is the Dale-Chall Readability Score?

The Dale-Chall Readability Formula is a test that measures reading difficulty or ease. It evaluates text based on two key factors: vocabulary difficulty and average sentence length. Unlike other formulas that rely heavily on syllable count (such as the Flesch-Kincaid Grade Level), the Dale-Chall formula uses a curated list of familiar words to determine a text’s complexity.

This makes it especially useful for evaluating content aimed at beginning readers or those with limited vocabularies. The lower the score, the more readable the content. The higher the score, the more challenging the text, making it better suited for advanced readers.

The Dale-Chall formula is widely used in education, publishing, and content development to ensure that written materials are appropriate for their intended audience.

What Is Readability and Why It Is Important for Web Content?

Readability is often defined as how well a piece of text matches the comprehension level of its intended audience. More specifically, readability refers to the ease with which a reader can understand written content. According to the Cambridge Dictionary, it is “the quality of being easy and enjoyable to read”.

Readability plays a crucial role in developing effective web content. Clear, accessible writing increases comprehension and ensures that information can be understood by a broad and diverse audience. According to the CSUN Universal Design Center, the more readable your web content is, the wider your audience reach becomes. 

Improving readability also promotes web accessibility. It helps ensure that users with cognitive disabilities, reading disorders, and non-native language backgrounds can access and understand your content. When language is overly technical or complex, it creates a barrier—not only for people with disabilities or language differences—but for all users.

Readability is also important for Search Engine Optimization (SEO). While not a direct ranking factor like keywords or backlinks, readability significantly impacts user experience and engagement, which do influence SEO performance. Well-written, easy-to-read content encourages users to stay on your site longer, explore more pages, and share content—actions that send positive signals to search engines.

According to Positional, an SEO and site audit tool, readability can directly enhance user experience and indirectly impact your Google rankings. They outline several metrics influenced by content readability, which search engines actively monitor:

• Time on page: How long visitors stay on a page.
• Engagement rate: Whether users interact with content or complete conversion events.
• Dwell time: How long a user remains on your site before returning to the search results.
• Scroll depth: How far users scroll down the page.

Summing up, if your content is unreadable, users won’t scroll down, stay on your page, or interact with your content. A high bounce rate, low engagement, and short session duration are all signs of poor readability—and they can hurt both user satisfaction and SEO performance. Prioritizing readability is essential for creating accessible, user-friendly, and search-optimized web content.

The Origins of the Dale-Chall Formula

In 1948, education professor Edgar Dale of Ohio State University and reading specialist Jeanne Chall developed the Dale-Chall Readability Formula. Their goal was to create a more accurate and reliable method for measuring text difficulty, particularly for use with school-aged children.

To achieve this, they conducted extensive research to identify words familiar to most students. The result was a list of approximately 3,000 common words that at least 80% of fourth-grade students in the U.S. could recognize. This word list became the foundation of the Dale-Chall formula and is still in use today—with some updates—to help estimate the difficulty level of texts based on word familiarity.

What made the Dale-Chall formula innovative at the time was its focus on vocabulary familiarity rather than more abstract linguistic features like syllable counts or sentence complexity alone. This word-based approach gave educators a practical tool to match reading materials to students’ comprehension levels, supporting better literacy development and academic progress.

How the Dale-Chall Test Works

The New Dale-Chall Readability Formula is a metric used to assess how difficult a text is to read. It does so by analyzing two main factors:

1. A predefined list of “familiar” words (about 3,000 words known by at least 80% of U.S. fourth-grade students).
2. The average sentence length.

The formula assigns a grade level that reflects the minimum U.S. school grade required to understand the text. Because it depends on a specific English word list, the Dale-Chall test is only applicable to English texts and will return a score of 0 for non-English content.

The two core components of the formula are:

• Percentage of Difficult Words (PDW): These are words not found on the Dale-Chall list. A higher percentage indicates a more complex text.
• Average Sentence Length (ASL): Calculated as the total number of words divided by the number of sentences. Longer sentences are generally harder to process.

The formula is as follows:

Raw Score = 0.1579 x (PDW) + 0.0496 x (ASL)

If the percentage of difficult words (PDW) is greater than 5%, an adjustment factor of 3.6365 is added to the score:

Adjusted Score = Raw Score + 3.6365 (if PDW > 5%)

Let’s look at a quick example:

– Total words: 200

– Sentences: 10

– Difficult words: 30

Step 1: Calculate PDW and ASL

• PDW = (30 / 200) × 100 = 15%
• ASL = 200 / 10 = 20

Step 2: Apply the formula

• Raw Score = 0.1579 × 15 + 0.0496 × 20 = 2.3685 + 0.992 = 3.3605

Step 3: Apply adjustment (since PDW > 5%)

• Final Score = 3.3605 + 3.6365 = 6.997

This score corresponds to a 7th–8th grade reading level in the U.S. educational system.

When to Use the Dale-Chall Readability Formula

The Dale-Chall Readability Formula is especially useful when clarity and simplicity are top priorities. Below are some of its most common applications:

• School Textbooks.  Teachers, curriculum developers, and textbook authors use the Dale-Chall formula to ensure that reading levels align with students’ grade levels. This helps prevent frustration caused by overly complex content and promotes more effective learning.
• Children’s Books. Authors and publishers of children’s literature use the formula to tailor sentence structure and vocabulary to suit specific age groups. This ensures that texts are both accessible and engaging, even for early readers.
• Government and Legal Documents. Public records, voting materials, legal notices, and health information must be clearly understood by the general public. The Dale-Chall formula helps ensure such documents are written in plain, accessible English.
• Web Content and UX Writing. Online users expect quick and effortless access to information. UX writers, web content creators, and app developers use readability tools like the Dale-Chall formula to make FAQs, onboarding messages, and user instructions easy to scan and understand.
• Technical and Scientific Writing. In fields like software documentation or user manuals, the Dale-Chall formula can help simplify complex content. For example, a platform like Drupal or other open-source projects can apply the formula to make technical guides more beginner-friendly and readable for non-experts.

Interpreting Your Dale-Chall Score

Once you’ve calculated your Dale-Chall Readability Score, you can interpret it using the following scale:

Value	School level	Student age range	Notes
4.9 or lower	Pre-kindergarten – 4th grade	3-10	Very easy to read.
5.0 – 5.9	4th grade – 6th grade	10-12	Easy to read. Conversational English for consumers.
6.0 – 6.9	6th grade – 9th grade	12-14	Fairly easy to read.
7.0 – 7.9	9th grade – 10th grade	14-16	Standard, plain English. Easily understood by 14- to 16-year-old students.
8.0 – 8.9	10th grade – 12th grade	16-18	Fairly difficult to read.
9.0 – 9.9	12th grade – college graduate	18-22	Difficult to read.
10 and above	University graduates	22 and above	Very difficult to read. Best understood by university graduates.

How to Use the Score

As a rule of thumb, aim for a score that matches—or is slightly below—your target audience’s reading level:

• If you’re writing for the general public, a score between 6.0 and 8.0 is usually ideal.
• If you’re writing for professionals or academic audiences, a higher score may be appropriate.

Remember, readability formulas only measure surface-level characteristics. A low score doesn’t automatically make your content effective. Writing can still be confusing or unclear if it’s disorganized, overly abstract, or off-topic.

Use the Dale-Chall formula as a guideline, not a rule. Combine it with good writing practices—clarity, coherence, structure—to truly improve your content’s accessibility and impact.

Conclusion

The Dale-Chall Readability Formula is an excellent tool for anyone who wants to write clearly and be understood. By focusing on common vocabulary and sentence structure, it provides a research-backed, meaning-focused way to assess how readable your writing is for a given audience.

Whether you’re a writer, editor, content strategist, or teacher, learning to apply the Dale-Chall formula can help you create copy that informs, engages, and resonates with your readers. In an age of short attention spans and a preference for clarity, those are skills well worth mastering.

Good luck with your technical writing!

ClickHelp Team

Author, host and deliver documentation across platforms and devices

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