Readability (Flesch Reading Ease)
Readability measures how easy a text is to read and understand. The Flesch Reading Ease test scores text from 0 (very hard) to 100 (very easy) based on sentence length and syllable count. WCAG recommends a Flesch-Kincaid Grade Level of 9 or lower (plain English) for web content, though specialised content may require higher levels.
§ 1 Definition
Readability in the accessibility context refers to how easily a reader can comprehend written text. The Flesch Reading Ease test, developed by Rudolf Flesch in the 1940s, calculates a score based on average sentence length (in words) and average syllables per word. Scores range from 0 (practically unreadable, academic-level text) to 100 (very easy, comic-level text). A score of 60-70 is considered plain English, roughly equivalent to an 8th-9th grade US reading level. The Flesch-Kincaid Grade Level converts this to a US school grade level. WCAG's Success Criterion 3.1.5 Reading Level (Level AAA) recommends that text not requiring specialised knowledge read at a lower secondary education level (grade 9 or below). While this is AAA level (not required for AA compliance), the practical guidance is: write simply and clearly for your audience. Even technical material can be structured with clear headings, short paragraphs, and plain language summaries.
§ 2 Why readability matters for accessibility
Cognitive disabilities affect reading comprehension, processing speed, and working memory. Users with dyslexia, aphasia, ADHD, and other cognitive conditions benefit enormously from simple, clear writing. But readability is not only about cognitive disability. Non-native speakers, people under stress, and anyone reading on a small screen also benefit from short sentences, common words, and clear structure. WCAG 3.1.5 Reading Level (AAA) exists because the web is for everyone, not just university graduates. The practical audit standard for AAA is the Flesch-Kincaid Grade Level test, widely available in tools like Hemingway Editor, Grammarly, and browser extensions.
§ 3 How to improve readability on the web
Use short sentences (15-20 words average). Replace jargon and technical terms with plain language alternatives, or define them on first use. Use active voice. Break long paragraphs into small chunks. Use descriptive headings and bullet points for scannability. Maintain consistent typography: line height of at least 1.5, line length of 45-75 characters, and sufficient font size (16px minimum recommended). Provide summaries of complex content. For legal, medical, or highly technical content (which may inherently have a high grade level), supplement with plain-language summaries, charts, and examples. The goal is not to dumb down content but to make it accessible to the widest possible audience.
§ 4 Common questions
- Q. Is Flesch-Kincaid Grade Level a WCAG requirement?
- A. WCAG 3.1.5 Reading Level (AAA) requires text to read at a lower secondary education level (grade 9 or below) if the text does not require specialised knowledge. This is a AAA criterion, not AA. Many organisations target AAA for general informational content while accepting higher grade levels for specialised content.
- Q. Does readability affect SEO?
- A. Yes. Readable content correlates with lower bounce rates, longer time on page, and higher engagement, all of which are positive SEO signals. Google's RankBrain algorithm also evaluates content clarity and relevance. Writing clearly for your audience is good SEO.
- Flesch Reading Ease scores text from 0 (hard) to 100 (easy); 60-70 is plain English.
- WCAG 3.1.5 (AAA) recommends grade 9 reading level or below.
- Short sentences, common words, active voice, and good structure improve readability.
- Readability benefits users with cognitive disabilities, non-native speakers, and everyone else.
- Readable content correlates with better SEO and user engagement.
Atomic Glue writes clear, accessible copy and structures content for readability as part of our Web Development services. We test content against readability benchmarks and provide plain-language alternatives where needed. Get in touch.
Get in touchReadability measures how easy a text is to read and understand. The Flesch Reading Ease test scores text from 0 (very hard) to 100 (very easy) based on sentence length and syllable count. WCAG recommends a Flesch-Kincaid Grade Level of 9 or lower (plain English) for web content, though specialised content may require higher levels.
Category: Accessibility (also: Content Strategy, UX)
Author: Atomic Glue Team
## Definition
Readability in the accessibility context refers to how easily a reader can comprehend written text. The Flesch Reading Ease test, developed by Rudolf Flesch in the 1940s, calculates a score based on average sentence length (in words) and average syllables per word. Scores range from 0 (practically unreadable, academic-level text) to 100 (very easy, comic-level text). A score of 60-70 is considered plain English, roughly equivalent to an 8th-9th grade US reading level. The Flesch-Kincaid Grade Level converts this to a US school grade level. WCAG's Success Criterion 3.1.5 Reading Level (Level AAA) recommends that text not requiring specialised knowledge read at a lower secondary education level (grade 9 or below). While this is AAA level (not required for AA compliance), the practical guidance is: write simply and clearly for your audience. Even technical material can be structured with clear headings, short paragraphs, and plain language summaries.
## Why readability matters for accessibility
Cognitive disabilities affect reading comprehension, processing speed, and working memory. Users with dyslexia, aphasia, ADHD, and other cognitive conditions benefit enormously from simple, clear writing. But readability is not only about cognitive disability. Non-native speakers, people under stress, and anyone reading on a small screen also benefit from short sentences, common words, and clear structure. WCAG 3.1.5 Reading Level (AAA) exists because the web is for everyone, not just university graduates. The practical audit standard for AAA is the Flesch-Kincaid Grade Level test, widely available in tools like Hemingway Editor, Grammarly, and browser extensions.
## How to improve readability on the web
Use short sentences (15-20 words average). Replace jargon and technical terms with plain language alternatives, or define them on first use. Use active voice. Break long paragraphs into small chunks. Use descriptive headings and bullet points for scannability. Maintain consistent typography: line height of at least 1.5, line length of 45-75 characters, and sufficient font size (16px minimum recommended). Provide summaries of complex content. For legal, medical, or highly technical content (which may inherently have a high grade level), supplement with plain-language summaries, charts, and examples. The goal is not to dumb down content but to make it accessible to the widest possible audience.
## Common questions
Q: Is Flesch-Kincaid Grade Level a WCAG requirement?
A: WCAG 3.1.5 Reading Level (AAA) requires text to read at a lower secondary education level (grade 9 or below) if the text does not require specialised knowledge. This is a AAA criterion, not AA. Many organisations target AAA for general informational content while accepting higher grade levels for specialised content.
Q: Does readability affect SEO?
A: Yes. Readable content correlates with lower bounce rates, longer time on page, and higher engagement, all of which are positive SEO signals. Google's RankBrain algorithm also evaluates content clarity and relevance. Writing clearly for your audience is good SEO.
## Key takeaways
- Flesch Reading Ease scores text from 0 (hard) to 100 (easy); 60-70 is plain English.
- WCAG 3.1.5 (AAA) recommends grade 9 reading level or below.
- Short sentences, common words, active voice, and good structure improve readability.
- Readability benefits users with cognitive disabilities, non-native speakers, and everyone else.
- Readable content correlates with better SEO and user engagement.
## Related entries
- [Accessibility (a11y)](atomicglue.co/glossary/accessibility)
- [Inclusive Design](atomicglue.co/glossary/inclusive-design)
Last updated July 2026. Permalink: atomicglue.co/glossary/readability