Now let's calculate the width of your document if you were creating a hardcover book, starting with the dimensions you calculated for a softcover. You must allow an added 1/8 inch on the spine for the cardboard. So the book calculated above would now have a spine size of 1 1/8 inches. To create the hinge area, located on both sides of the spine, you must add another 7/16 of an inch to your document for both the front and back covers. You must then add the page width dimension and add an extra 5/8 inch to allow for the area that folds over the cardboard. You then have the final width needed for your document. Calculating the height is much easier. Simply take the height of your page, in this case 9 inches and add an extra 5/8 inch on both the top and the bottom to allow for the wrap over the cardboard.