How Many Wallpaper Rolls Do I Need? Pattern Repeat Math
Wallpaper is sold in rolls, hung in drops, and ruined by mismatched patterns. The arithmetic that gets the count right the first time.
Measure the room, not the wall
Measure the perimeter of every wall you will paper (skip door and window openings under 0.5 m², they become your error margin) and the floor-to-ceiling height. Area alone is not enough: rolls are consumed drop by drop, so the count comes from lengths, not square metres.
What a double roll actually is
North American wallpaper is priced per single roll but packaged and shipped as double rolls. A standard double roll is 27 in wide × 27 ft long = 60.75 sq ft ≈ 5.6 m²; a single roll is half of that — 27 in × 13.5 ft, about 2.8 m². You cannot buy a lone single: order four singles and two double rolls arrive. The European standard roll (0.53 m × 10.05 m ≈ 5.33 m²) is close to one US double roll, which is why the same paper can legitimately show a different roll count on each side of the Atlantic.
Where the confusion costs money
Two shops can quote the same price per roll and still differ by a factor of two in coverage if one means single and the other double. Three checks settle it: find the coverage figure in sq ft or m² — the only number that matters — then sanity-check it as length × width, and compare price per square metre rather than per roll. And when a calculator returns singles while the shop sells doubles, halve the count: 8 singles to order = 4 double rolls.
Pattern repeat: the real waste multiplier
The repeat is the vertical distance until the pattern lines up again. Straight-match papers strip out with almost no repeat waste. Drop (half-drop) match shifts every second strip, so each strip must be cut one repeat longer than the wall height and the offcuts rarely reuse. Round down: usable strips per roll = roll length ÷ (wall height + repeat) for drop match, and roll length ÷ wall height for straight match. Example: 10.05 m roll, 2.5 m wall, 0.26 m repeat → 10.05 ÷ 2.76 = 3 strips per roll instead of 4.
Worked example: a 3.6 × 4.2 m room
Perimeter (3.6 + 4.2) × 2 = 15.6 m; at a 2.5 m ceiling height the gross wall area is 39 m². Subtract the door (≈1.8 m²) → 37.2 m². Add 10–15% for repeat trimming and miscuts → ≈42 m². European rolls: 42 ÷ 5.33 = 7.9 → 8 rolls. US double rolls: 42 ÷ 5.6 = 7.5 → 8 doubles = 16 singles. If the shop prices per single roll, order 16 — they arrive as 8 double rolls.
Always buy the same dye lot
Colour varies between production batches. Order every roll for a room in one purchase, check that the lot numbers match on the labels, and add a spare roll — 10% extra for plain papers, 15–20% for large repeats. Discontinued dye lots cannot be matched later.
Run the numbers once
The Wallpaper calculator takes perimeter, height, openings and roll presets (including pattern repeat), works out drops per roll and roll count, and adds the safety margin for you.