Question

What is
default paper size used
in Office​

Answer 1

8.5 x 11 inches

Word's default paper size is “Letter,” which is 8.5 x 11 inches. If you use a different size more frequently than the default, you can change the default size of all new documents. This way, you won't have to change the paper size of each new document you create. To do this, go to Layout > Size > More Paper Sizes.