Wallpaper Calculator
Rolls needed, accounting for the pattern repeat.
How it works
Wallpaper is counted in strips, not in square metres. Work out how many full strips a roll yields — roll length divided by the height of one strip — then how many strips the perimeter needs. Rounding down on the first division and up on the second is what makes the answer correct.
The pattern repeat is what wastes paper. If the design repeats every 64 cm, each strip must be cut to the next whole multiple of that, so a 2.7 m wall can require a 3.2 m strip. A plain paper with no repeat wastes almost nothing, which is why it works out considerably cheaper than the roll price suggests.
Related calculators
How the Wallpaper Calculator works
A wallpaper calculator counts rolls through strips rather than through area. That is what makes the answer correct: a roll cuts into whole strips, and what is left over at the end of it cannot be used.
Strips, not square metres
Calculating by area consistently under-orders. The right sequence is different: first work out how many whole strips a roll yields — roll length divided by strip length, rounded down. Then how many strips the perimeter needs — perimeter divided by roll width, rounded up. Divide the second by the first, rounding up again.
Rounding down in the first step is the crucial part. If a 10.05 m roll yields three 2.8 m strips, 1.65 m is left over and will not make a fourth. That metre and a half is paid for and thrown away — an area calculation never sees it.
The pattern repeat is what wastes paper
The repeat is the interval at which the design recurs. If it is 64 cm, every strip must begin at the same point in the pattern, so it is cut to the next whole multiple of the repeat. A 2.7 m wall with trim needs a 3.2 m strip instead of 2.8 — nearly half a metre wasted on every strip.
This is why plain and free-match papers work out considerably cheaper than the roll price suggests. With a large repeat and a fixed budget, the difference in final cost can exceed the difference in price per roll.
FAQ
How many rolls for a 20 m² room?expand_more
A 5 × 4 m room has an 18 m perimeter. In 1.06 m wide paper that is 17 strips. At 2.7 m plus trim each strip is 2.8 m, and a 10.05 m roll yields three of them — so 6 rolls. A 64 cm repeat stretches the strip to 3.2 m, which still fits three times, so here it changes nothing. Raise the ceiling to 3.2 m and the same repeat pushes the strip to 3.84 m: only two per roll, and you need 9.
Should I subtract windows and doors?expand_more
Usually not, and that is not an oversight. The pieces above and below an opening are still cut from full strips, and the offcuts rarely get used. Only subtract openings when there is very large full-height glazing.
How much trim should I allow?expand_more
5 cm top and bottom, so 10 cm per strip. Ceilings and floors are seldom truly level, and the allowance lets you align the strip to the pattern rather than to a crooked ceiling. Only experienced hangers work without it, and only on perfectly square walls.