[WATS.ca Archived]

July 2, 2014

Readability and its Implications for Web Content Accessibility


Back in the early 2000′s, my colleague and friend Derek Featherstone and I launched a joint consultancy group in Ottawa, Canada that focused on the issues of on-line accessibility, and the emergent techniques and requirements of this (at the time) new aspect of web development. Derek and I wrapped up WATS.ca somewhere around 2006 as we moved on to other projects, but we both remain active in the field today.

We jointly published a number of articles on our web-site that often became go-to references then, and it seems a shame that they be lost to the vagaries of time; the original site long since gone. I have created an Archive section of this site to preserve those postings, and the following article from that time is one such. Please note that some of the information in this or other similar articles may be dated, or superseded by events in time: I am making no attempt to update these articles and am simply posting them as they existed when they were first written.

By: John Foliot | Posted: November 17, 2005

One area of accessibility often overlooked is the readability of the content of your web pages. Not every user may be familiar with terms or terminology being used. Others may not have the same socio-political background, literacy skills or capacity to fully comprehend what it is you are saying. One goal of the content author then is to try and identify their target audience, and then ensures that they are not “writing over their heads”.

Remember Though – It’s More Than Just a Number

Readability indexes are helpful, but they do not consider the best motivator of all: interest in the material. People will read at a much higher level the things they find interesting. It may prove helpful to recruit a few people from within your group or organization that don’t typically work with or on the topic you are writing about and ask them to read the copy. It’s likely they will provide you with the most valuable feedback on readability.

Performing Your Readability Checkup

There are many ways to gauge readability, but the Flesch Readability Index and Flesch-Kincaid
Grade Index are two or the more commonly used in the corporate world. Software is now available that will score documents using a variety of methods. Most content writers already have the basics to check readability: a word processing application. Microsoft Word, for example, can analyze documents using both Flesch methods, as well as provide you with several other document facts.

Other word-processing software packages also measure readability using the Flesch indexes and other methods. For information specific to your word-processing software, perform a search of the program’s help files using the keyword “readability”.

A number of methods or indexes have been developed to help determine the comprehension level of written material, and three of the most popular are listed below:

Flesch Reading Ease Score

This computes readability based on the average number of syllables per word and the average number of words per sentence, and is calculated by the following equation:

206.835 – (1.015 * Average_words_per_sentence) – (84.6 * Average_syllables_per_word)

The formula requires only sentence and syllable data, but creates a very reproducible and predictable score.
Scores range from 0 (zero) to 100. Standard writing averages approximately 60 to 70. The higher the score, the greater the number of people who can readily understand the document. For example, the average Reading Ease score for comic strips is 92. The Readers Digest has an average score of 65. The Wall Street Journal has an average score of 43, while The Harvard Law Review has an average score of 32. Standard Insurance Policies have a dismal average score of 10.

Rudolf Flesch was trained as a lawyer in his native Vienna. He came to the United States in 1938 where he received his PhD at Columbia University. Among his numerous books are The Art of Plain Talk, Say What You Mean, The Art of Clear Thinking, and The Art of Readable Writing (Harper & Row). Flesch developed the algorithm over several years of research, and earned a PhD for the work.

Reader Feedback:

For unexplained reasons, Microsoft’s version of the Flesch-Kincaid does not score above grade 12, although the original formula scored up to a graduate school level. Since any grade level above 12 will be reported as grade 12, documents at a graduate school reading level will be reported as grade 12 – a measurement error of about 7 grades. Since all research relying on Word’s Flesch-Kincaid formula seriously underestimates a document’s grade level, all of the research done on health materials using Word’s Flesch-Kincaid is seriously flawed.

More information about the Flesch-Kincaid formula can be found on Microsoft’s web site at:

Several readability researchers have contacted Microsoft about this problem, but the company has neither acknowledged the problem nor fixed it.

Researchers relying on readability statistics should consider other programs, such as Readability Calculations (www.micropowerandlight.com), SpellCatcherPlus (www.rainmakerinc.com), or GrammarExpert Plus (www.wintertree-software.com), or the readability formulas in WordPerfect.

Make sure that your readability software accurately measures readability. Before putting your trust (and your reputation) into any readability software, analyze a few documents by hand and compare your results to the software.

Submitted by: Mark Hochhauser, Ph.D. – Readability Consultant MarkH38514@aol.com

Flesch-Kincaid Grade Level Score

Computes readability based on the average number of syllables per word and the average number of words per sentence. A score of 5.0 for example indicates a grade-school level, a score of 8.0 means that an eighth grader would understand the document. Standard writing approximately equates to the seventh-to-eighth-grade level.

The formula for the Flesch-Kincaid Grade Level score is:

(.39 x ASL) + (11.8 x ASW) – 15.59

Where ASL = “average sentence length” (the number of words divided by the number of sentences), and ASW = “average number of syllables per word” (the number of syllables divided by the number of words).

Gunning Fog Index

Gunning Fog Index (the easiest to use and probably the most popular readability index) is a proven method of analyzing written material to see how easy it is to read and understand. The steps you can use to calculate the Fog Index are outlined below. The numbers in the right column are based on this paragraph. When using these steps to analyze your writing, choose a sample that contains at least one hundred words. The “ideal” Fog Index level is 7 or 8. A level above 12 indicates the writing sample is too hard for most people to read.

Steps in Applying the Index

  • Select a sample
  • Determine the average number of words per sentence
  • Determine the percentage of hard words
  • Add the 2 factors and multiply by 0.4

The result is the minimum grade level at which the writing is easily read!


In general, construction of pictograms follows the general procedure used in constructing bar charts. But two special rules should be followed. First, all of the picture units used must be of equal size. The comparisons must be made wholly on the basis of the number of illustrations used and never by varying the areas of the individual pictures used. The reason for this rule is obvious. The human eye is grossly inadequate in comparing areas of geometric designs. Second, the pictures or symbols used must appropriately depict the quantity to be illustrated. A comparison of the navies of the world, for example, might make use of miniature ship drawings. Cotton production might be shown by bales of cotton. Obviously, the drawings used must be immediately interpreted by the reader.


129 words in 10 sentences = asl of 13

26 hard words out of 129 = 20%

Average sentence length 13.0
Percentage of hard words 20.0
Total 33.0
Multiply by 0.4

Grade level of readership – 13.2

Using the Indexes

The use of these types of indexes is useful in establishing overall readability. However, content authors are cautioned to use them in moderation, they are but tools, not arbitrators, and should be employed as such.

Indexes are popular because they:

  • reduce to simple formulas the complex work of writing
  • provide a convenient check and measure of the level of one’s writing
  • possess the glitter of mathematical exactness
  • can be calculated by word processing software

Indexes limitations:

  • a low style of writing can result from a slavish use of readability indexes – a monotonous succession of short sentences and simple words can make your writing dull and dull writing doesn’t hold the reader’s attention
  • the indexes frequently give conflicting results

Best use of Indexes:

Posted by John

I am a 16 year veteran of Web Accessibility, living and working in Austin, Texas. Currently Principal Accessibility Strategist at Deque Systems Inc., I have previously held accessibility related positions at JPMorgan Chase and Stanford University. I am also actively involved with the W3C - the international internet standards body - where I attempt to stir the pot, fight hard for accessibility on the web, and am currently co-chairing a subcommittee on the accessibility of media elements in HTML5.

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