How wallpaper roll calculator works
Wallpaper is sold by the roll but hung by the strip, so the math has to think in strips. Enter the total wall area you plan to paper and the ceiling height; the calculator subtracts openings like doors and windows from the area, derives the total wall run (net area divided by height), and divides that run by the roll width to count how many vertical strips the job needs.
Each strip is cut longer than the wall is tall when the paper has a pattern. If you enter a pattern repeat, every strip is rounded up to the next whole multiple of the repeat so adjacent strips line up — that trimmed waste is real, and it is where most underbuying happens. Strips per roll is then roll length divided by usable strip length, floored to a whole number because a roll cannot be spliced mid-strip.
Finally the strip count is divided by strips per roll and rounded up: rolls to buy. Defaults reflect common stock — a 16 ft × 27 in American roll in imperial, or a 10 m × 53 cm European roll in metric — but every roll dimension is editable, because speciality papers vary widely and buying one roll short means a dye-lot mismatch you cannot fix later.