How many rolls of wallpaper do I need?
The maths is simple: wall length × wall height = wall area, then divide by the coverage printed on the roll and round up. The part people get wrong is the waste allowance. A roll's stated coverage assumes you can use every inch of it, but you can't — each drop has to be cut to the wall height, and on a patterned paper each drop also has to be shifted so the pattern lines up with the one beside it. That offset is the pattern repeat, and the taller the repeat, the more paper ends up in the bin. A plain or textured paper wastes very little, so 10% is enough. A small repeat under about 6 inches usually lands near 15%. A large repeat, or a straight-across match on a bold print, can easily push waste to 25%.
Two practical points. First, don't subtract doors and windows unless they're genuinely large, like patio doors or a picture window — an ordinary door or window is roughly one drop's worth of paper, and you'd have cut around it anyway. Leaving them in gives you a sensible buffer. Second, buy all your rolls at once and check that the batch or dye-lot number matches on every one. Colour shifts slightly between print runs, and a mismatched roll is obvious on a finished wall. If you're ordering online, one spare roll costs far less than reordering later and getting a different batch.
Roll sizes vary a lot by market and by brand (European rolls, American single and double rolls all differ). Always check the coverage on the label rather than assuming, and confirm quantities with your supplier before ordering.