Wallpaper Calculator

Roll coverage on the label is theoretical: a US double roll is about 56 sq ft of paper, but once every strip has to be cut so its pattern lines up with the strip beside it, usable coverage drops. A small or random repeat wastes little; a large repeat can cost 15–25% of every roll in offcuts. That is why this calculator adds 15% before dividing by roll coverage.

Total wall area is 360 sq ft, less 15 sq ft for each of three openings, leaving 315 sq ft. Without a waste factor, and at 28 sq ft of usable coverage per roll, that is 12 rolls; with the 15% pattern allowance it becomes 13. Buy the thirteenth even if the twelfth looks like it will stretch — running a strip short at the last corner means ordering into a new dye lot.

Professionals work in drops: divide the wall width by the roll width, usually 20.5 or 21 inches, to get the number of strips, then work out how many full-height drops each roll yields. A 9 ft wall from a roll holding 33 ft of paper gives three drops with 6 ft left over — or only two, if the pattern repeat forces you to waste a length getting the alignment right.

Dye lots vary visibly between print runs, so order every roll at once with matching batch numbers, plus one spare for future repairs. Subtract only generously sized openings from your area: the strips above a door and beside a window still consume close to full lengths, so deducting the true area of small windows is the most common way people end up a roll short.

Wallpaper telegraphs whatever is underneath it. Fill and sand first, then size or prime the wall so paste doesn't soak into porous drywall and so the paper can be stripped later without tearing the surface. Hang your first drop against a plumb line rather than a corner — walls are rarely square, and an out-of-plumb start compounds across the room.