Sentence length

This resource is an archived version of the Readability Guidelines.

New wiki is at:
Go to the Simple sentences page.


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

2. 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." GOV.UK

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."

Writing for GOV.UK, UK Government website

'Sentence length: why 25 words is our limit', Inside GOV.UK, UK Government blog, 2014

'Content design', Sarah Richards, 2017

'The role of word difficulty and sentence length in text comprehension', T. M. Duffy and P. K. U'Ren, 1982

'The Influence of Semantics and Syntax on What Readers Remember', C. S. Isakson and J. H. Spyridakis, 1999

Reading Level, Understanding SC 3.1.5, WCAG, 2008

'Readability Assessment of Internet-Based Consumer Health Information', T. M. Walsh and T. A. Volsko in Respiratory Care October 2008, 53 (10) 1310-1315

'The research basis of plain language techniques: Implications for establishing standards', Karen Schriver, PhD, Dr. A. L. Cheek, M. Mercer, Center for Plain Language, November 20, 2008, Mexico City

'Readability Levels of Health-Based Websites: From Content to Comprehension', M. Schutten, A. McFarland, PhD, International Electronic Journal of Health Education, 2009, 12:99-107

'Writing smaller', Clarity Journal no. 63, 2010

Plain Language Commission style guide, 2012

'Shorter Lines Facilitate Reading in Those Who Struggle', Matthew H. Schneps , Jenny M. Thomson, Gerhard Sonnert, Marc Pomplun, Chen Chen, Amanda Heffner-Wong, 2013

'Towards a better measure of readability: Explanation of empirical performance results', Leslie A. Olsen & Rod Johnson, Taylor & Francis Group, 2015

'What is plain language?', Plain Language Association International, 2015

Text complexity, ATOS, and Lexile® Measures, Renaissance Learning, 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?' Edwin Toonen, Yoast, 2018

The Crystal Mark standard Plain English Campaign, undated

Related wiki pages

Sentence structure
Plain English

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License