How to Set Word to US Letter Size
A US letter-size piece of paper is 8.5 inches wide by 11 inches long. Most businesses and organizations in the United States use US letter-size paper for their printing and copying needs. By default, Microsoft Word uses US letter-size paper, but if you're using the program on another computer or you accidentally change the setting, you can easily reset it to US letter-size in the Page Layout section.
Launch Microsoft Word and open your document.
Click the "Page Layout" tab on the toolbar at the top of the window.
Click "Size" in "Page Setup." Select "8.5 x 11 Letter."