Sentence length


Keep sentences to 15 words on average and not longer than 25 words.

Split up longer sentences to make them clearer: create more than 1 sentence or use bulleted lists.

Usability evidence

"People with some learning disabilities read letter for letter – they do not bounce around like other users. They also cannot fully understand a sentence if it’s too long. People with moderate learning disabilities can understand sentences of 5 to 8 words without difficulty. By using common words we can help all users understand sentences of around 25 words."

'Content design' by Sarah Richards, 2017, includes the following references:

  • The Oxford Guide to Plain English recommends 15–20 words per sentence. It also says: "…if you regularly exceed 40 words, you’ll certainly weary and deter your readers."
  • Jyoti Sanyal, author of 'Indlish' said: "Based on several studies, press associations in the USA have laid down a readability table. Their survey shows readers find sentences of 8 words or less very easy to read; 11 words, easy; 14 words fairly easy; 17 words standard; 21 words fairly difficult; 25 words difficult and 29 words or more, very difficult."
  • Author Ann Wylie said: "When the average sentence length in a piece was fewer than 8 words long, readers understood 100% of the story. At 14 words, they could comprehend more than 90% of the information. But move up to 43-word sentences and comprehension dropped below 10 percent."

'The role of word difficulty and sentence length in text comprehension', 1982

'The Influence of Semantics and Syntax on What Readers Remember', 1999

WCAG Reading Level, 2008

'Readability Assessment of Internet-Based Consumer Health Information', 2008

'The research basis of plain language techniques: Implications for establishing standards', 2008

'Readability Levels of Health-Based Websites: From Content to Comprehension', 2009

Clarity Journal no. 63 'Writing smaller', 2010

Plain Language Commission style guide, 2012

'Shorter Lines Facilitate Reading in Those Who Struggle', 2013

'Sentence length: why 25 words is our limit', 2014

'Towards a better measure of readability: Explanation of empirical performance results', 2015

'What is plain language?', 2015

Text complexity, ATOS, and Lexile® Measures, 2016

'Understanding Plain English summaries. A comparison of two approaches to improve the quality of Plain English summaries in research reports.' 2017

'How to use Yoast SEO: The readability analysis?' 2018

The Crystal Mark standard. No date

Related wiki pages

Sentence structure
Plain English

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