Wallpaper Rolls Needed: Usable Coverage Per Roll
Bigger pattern repeats waste more paper, so room size, openings, and roll type here become a roll count that already covers the extra matching material.
How it works
Wallpaper starts like paint: room perimeter times ceiling height gives the wall area, and doors and windows are deducted. The difference is what a "roll" actually covers. The square footage printed on the roll is the paper's face area, but you never use all of it — you trim the top and bottom to the wall, and on a patterned paper you waste a strip at every seam matching the repeat.
So the calculator divides by usable coverage, not label coverage. A US single roll holds about 28 sq ft but yields roughly 25 sq ft usable; a double roll (bolt) holds about 56 sq ft and yields about 50. Most wallpaper is sold and priced as double rolls even when packaged as two singles.
The pattern repeat is handled through the waste allowance. A small or random-match pattern wastes little, so 10 % is enough; a large drop-match repeat can waste far more, so bump it to 15 % or 20 %. Rolls round up, and buying from one run keeps the color consistent.
perimeter = 2 × (12 + 14) = 52 ft → gross wall = 52 × 8 = 416 sq ft
openings = 21 + 2 × 15 = 51 sq ft → net wall = 365 sq ft
rolls = 365 × 1.15 ÷ 50 = 8.4 → 9 double rolls