Wallpaper roll calculator

A drop is one floor-to-ceiling strip. Full-width drops are hung and trimmed around openings, so opening widths are not deducted from the drop count; the short pieces above and below doors and windows are instead cut from the offcut ends of already-opened rolls before any new roll is counted. Leftovers on rolls opened for short pieces count as waste, and the spare roll stays uncut. What this tool does not do: it cannot match pattern across outside corners, it ignores roll width variations between batches, and it does not check that your walls are truly rectangular.