Work out how many wallpaper rolls a room needs with pattern repeat matching.
Wallpaper is counted in drops, not in area, because a roll is cut into full-height strips and whatever is left at the end of the roll is waste. Divide the wall perimeter by the roll width to get the number of drops, then work out how many drops a roll yields: roll length divided by drop length, rounded down. The pattern repeat is what makes this different from paint — to match the design at every seam you have to cut each drop to the next whole repeat, so a 21 inch repeat on an 8.5 ft wall means cutting at roughly 10.5 ft and losing nearly two feet per drop. That is why a large-repeat paper can need 30% more rolls than a plain one on the same wall. Always buy from a single batch number, and one roll more than the calculation says.
Wallpaper Roll Count
Drop length = wall height + pattern repeat/12 + 0.5 ft trim; drops = perimeter x 12 / roll width, less one per opening; drops per roll = roll length / drop length, rounded down; rolls = drops / drops per roll
For a typical 46 ft perimeter room at 8.5 ft high with a 21 in repeat and two openings, about 8 to 9 standard European rolls. A plain paper on the same walls needs 6 or 7.
Because every drop must start at the same point in the design. If the repeat is 21 inches and the wall is 102 inches, each drop is cut at 126 inches — two feet of it goes in the bin.