Adding Readability Statistics to Outlook Spelling and Grammar

Microsoft Outlook 2007 and Outlook 2010 allow users to view Readability Statistics when they run Spelling & Grammar checking on an email message. This feature is a product of Microsoft Word serving as the email editor in Outlook 2007 and 2010.

 Readability Statistics are not enabled by default in Outlook (nor are they in Word). This option is easily activated through a checkbox in the Options settings. You navigate to the Outlook 2010 backstage by selecting File, Options, or in Outlook 2007, select Tools, Options from the main interface. In Outlook 2010, you select Mail on the left side menu and then the Spelling and Autocorrect button. In Outlook 2007, click the Spelling tab and then the Spelling and Autocorrection button. In order for Outlook to determine readability, it must also check for grammar. Select the check box beside “Check grammar with spelling.” This enables the “Show readability statistics” setting. Now you can select the check box next to “Show readability statistics,” and then click OK. The change takes effect immediately. Figure 1 shows both of these options circled in red.

 When you compose a new email message and run the Spelling & Grammar function from the Review tab of the Office Ribbon, Outlook will scan for spelling and grammar errors and then present a Readability statistics summary as shown in Figure 2. The output of this scan includes item counts of words and sentences for the email, as well as three readability results. What’s missing from this output is the number of syllables. The actual readability formulas use syllables in their calculations.

 Readability tests try to assess a relative level needed to comprehend written text. There are many such tests that are used to evaluate writing. Developed by Austrian Rudolf Flesch in the 1940s, the Flesch Reading Ease test is one of the more common ones. It employs the following formula:

 FRE = 206.835 – (1.015 x ASL) – (84.6 x ASW)


  • FRE = Flesch readability ease
  • ASL = Average sentence length (average number of words per sentence)
  • ASW = Average syllables per word

 The lower the FRE, the higher the level of English comprehension is required to understand the text. In my example, a value of 55.6 was reached. Roughly, the scale values of 0-30 are considered college level; 30-60 falls in the senior high school level; 60-70 is junior high level; and 70-100 is elementary level.

The Flesch-Kincaid Grade Level Readability Formula is also fairly simple. John R. Kincaid expanded the work of Flesch and computed a grade level of readability, which is used in education and by the U.S. Department of Defense. The formula works as follows:

 FKGL = (0.39 x AWS) + (11.8 x ASW) - 15.59


  • FKGL = Flesch-Kincaid grade level. This value typically falls between 1 and 12; however, extreme cases can take the result beyond this scale in either direction.
  • ASL = Average sentence length (average number of words per sentence)
  • ASW = Average syllables per word

 Outlook also includes a Passive Sentence Ratio. Readability improves with a lower ratio of Passive to Active sentences. Figure 2 shows the Passive Sentences ratio for my article as 11%.

Of course, the goal is not to attain the highest grade level or the lowest reading ease level, but rather to write to the audience. A research lab may write to a higher level than an entertainment agency. Checking readability for emails may be beneficial for managers to help ensure their audience understands the message. Just for fun, you could take those memo emails from the CEO and check the readability or even compare between managers.

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