Wallpaper Calculator

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.