One single roll of wallpaper yields approximately 25 square feet of usable paper, regardless of its width. Wallpaper is priced by the roll but is often sold in bundles of two or three rolls.
To determine the approximate square feet of wallpaper needed, add together the length of each wall and multiply that number by the height of the walls. Compute the square footage of each window or door on the wall and subtract that number from the total. Finally, multiply the result by 1.15 to account for waste due to repeated patterns and matching, which is approximately 15 percent for the entire project.