Answer
This is an excellent question. all the other answers are nice but the best way to determine how much wallpaper you will need is by determing the "repeat" of "pattern run" or the paper. this means how often the pattern repeats itself. you will never truly know how much paper you will need until you figure this out. when wallpapering you want to line up the pattern on the walls so you cannot see where the seams are. the result is extra, wasted paper but a great looking wall with hidden seams. rolls with repeating patterns will indicate this on the roll or on the back of the paper sample in wallpaper books. once you know the repeat, then you can determine how much paper you need to do a room. of course, you will need the measurements of the room and the height of the ceiling. you need to treat doors and windows as if they were a wall to make sure you have enough paper. nice luck!
