Wallpaper counted in drops, not square feet

Because paper comes off the bolt in one continuous length and a wall is cut in fixed lengths, so the leftover at the end of every bolt is unusable no matter how much square footage it represents. A 33 ft bolt asked for 10 ft 6 in drops gives three and leaves 18 in that cannot become a fourth. On a 14 by 12 ft room at 8 ft 6 in the area sum says eight bolts and the drop count says eleven, and three bolts is not the kind of gap a ten percent waste allowance rescues. The area method also cannot see the pattern at all, which is the other half of the problem.

It is the vertical distance before the design starts over, printed on the bolt label beside the match type and usually between 0 and 36 inches. Its whole significance is that a drop has to be cut to a whole number of repeats so that the design meets the drop beside it at the same height, which means the cut length is the wall height rounded up rather than the wall height. A 25 in repeat on an 8 ft 6 in wall forces a 10 ft 5 in cut and throws away nineteen inches at the bottom of every drop, before a single seam has been hung.

Half a repeat off each bolt if you cut it properly, and half a repeat off every drop if you do not. Consecutive drops cut from one bolt land back on exactly the same point in the design, so they are the odd drops or the even drops but never both — cut three off a bolt and hang them as drops 1, 3 and 5 round the room, and the parity costs you nothing after the first cut. Work through the bolt in hanging order instead and every second drop needs half a repeat run off first. That is the difference between eleven bolts and fifteen on a typical room, and it is a sequencing decision rather than a material one.

No, and deducting them is how orders come up short. A window leaves wall above it and wall below it, and each of those pieces has to begin at its own point in the design to line up with the full drop beside it, so a 3 ft window turns one long cut into two short ones that cannot both come from the same offcut. Doorways are different because there is nothing below them: a doorway wider than the bolt swallows a whole drop and leaves only the piece over the head, which is why this page deducts whole bolt widths inside a doorway and nothing else.

Paste-the-wall papers have a non-woven backing that does not expand when it is wet, so the paste goes on the wall and the dry drop is hung straight onto it. Traditional paper backings do expand — by up to half an inch across a 20.5 in width — which is why paste-the-paper stock has to be pasted, folded and left to book for the number of minutes on the label so that the swelling finishes before the drop reaches the wall. Hanging a booked paper too soon puts the expansion into the seam, which then opens as it dries. The choice does not change the roll count, but it changes whether you need a pasting table and it decides how well the paper strips off in ten years.

Yes — check the run or batch number on every label before leaving the counter. Wallpaper is printed in runs and the ink is mixed per run, so two bolts of the same pattern from different runs are close enough to pass on the shelf and visibly different where they meet on a seam. That is also the case for ordering the spare at the same time rather than later: a reprint six months on will not match, so the offcut you keep rolled in a closet is the only repair material that ever will.

Two inches at each end is the working default and it is doing two jobs at once. Part of it is slack for sliding the drop up or down until the pattern meets its neighbor; the rest absorbs a ceiling line or a floor that is out of level, which almost every house older than about thirty years has. It is also the single most leveraged number on this page, because the cut length is rounded up to the repeat afterwards: on an 8 ft 6 in wall with a 21 in repeat, going from two inches to one at each end drops the cut from 10 ft 6 in to 8 ft 9 in and saves a full repeat on every drop.