How it is calculated
Wallpaper is counted in strips, not in square metres. The calculator finds the length of wall to cover (the perimeter minus doors), divides it by the roll width to get the number of strips, and works out how many full strips one roll gives at your wall height plus 10 cm for trimming. A pattern repeat makes every strip longer, rounded up to a whole repeat. Windows are not subtracted: the pieces above and below them use up the off-cuts.
Strips = (perimeter − doors × 0.9 m) ÷ roll widthStrips per roll = roll length ÷ (wall height + 0.1 m, rounded up to the repeat)Rolls = strips × (1 + reserve) ÷ strips per rollExample
A room of 4 × 3 m with a 2.6 m ceiling and one door needs 25 strips of 0.53 m. A 10.05 m roll gives three 2.7 m strips, so with a 5 % reserve you need 9 rolls.
Tips from practice
- Check that every roll has the same batch number on the label.
- Large repeats (over 30 cm) can add one or two rolls to a room — always enter the repeat.
- Keep one spare roll for repairs; shops often accept unopened rolls back.
Questions and answers
How many rolls for a 12 m² room?
A 4 × 3 m room with a 2.6 m ceiling usually needs about 9 standard rolls (0.53 × 10.05 m) without a large pattern repeat.
What is a pattern repeat?
It is the distance after which the pattern repeats vertically. It is printed on the label, for example 64 cm. Each strip has to start at the same point of the pattern, so you lose some length.
Are wide rolls more economical?
Wide 1.06 m rolls mean fewer seams and faster work. The amount of material is similar, but large repeats waste more with wide rolls.
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