First, copy and paste the text you'd like to see checked into Word (tm)
Next, choose the drop down arrow located next to spell check icon at the top. Choose more commands from the drop down pane.
Next, you'll choose the word that says Proofing on the side panel.
Scroll down after selecting proofing and make sure show READABILITY STATISTICS and grammar & refinements has been selected.
Next, recheck your document if you hadn't before.
After your document has been checked a Readability Statistics box will show up. It lists for you the total words, average words per sentence, the reading ease, as well as the Flesch-Kincaid Readability.
