Wallpaper Calculator
Wallpaper is counted in drops off a roll, not by area. The pattern repeat lengthens every drop, which is why a patterned paper can need two more rolls than a plain one on the same wall.
Rolls needed
9rolls
- Drops needed
- 26
- Cut length
- 2.56 m
- Drops per roll
- 3
- Wasted per drop
- 12.2 cm
- Wall perimeter
- 44.0 ft
- The pattern repeat costs 12.2 cm off every drop, because each one has to start at the same point in the pattern.
- Doors and windows are not deducted. The offcuts go above and below them, and deducting a standard opening is how people end up a roll short.
- Buy every roll in one order and check the batch number on each. Colour shifts between print runs and a mismatched roll shows on the wall.
About the wallpaper calculator
Every other material in this category divides an area by a coverage figure. Wallpaper does not work that way, and treating it as though it does is why so many people end up one roll short with the pattern discontinued.
A roll is a fixed width and a fixed length. You get whole drops out of it or you get nothing usable, because the piece left at the end of a roll is almost always too short to reach the ceiling. A standard roll is 10.05 metres long, so at a 2.44 metre drop you get four out of it and 0.29 metres is wasted.
The pattern repeat is what really bites. On a patterned paper every drop must start at the same point in the pattern, so a drop is not the wall height — it is the wall height rounded up to a whole number of repeats. An eight-foot wall in a paper with a 32cm repeat needs a 2.56 metre cut, and that extra 12cm comes off every single drop. It takes the yield from four drops a roll down to three, and the same room goes from seven rolls to nine.
Doors and windows are deliberately not deducted. The trade does not deduct them for standard openings, because the offcuts are what go above and below them. Taking a door off the area is another way to finish a roll short.
What it works out
- Rolls needed, counted in whole drops
- Pattern repeat, and free, straight or offset matching
- Any roll width and length, metric or imperial rolls
- The cut length and what each drop wastes
The formula
Rolls = ⌈Drops ÷ ⌊Roll length ÷ Cut length⌋⌉, where Cut length = ⌈Height ÷ Repeat⌉ × Repeat
Three steps, and each one rounds.
First, how many drops go round the room: the perimeter divided by the roll width, rounded up. A twelve by ten room is 13.41 metres round, and at 53cm wide that is 26 drops.
Second, how long each drop has to be cut. On a plain paper it is the wall height. On a patterned one every drop has to start at the same point in the pattern, so the cut length is the height rounded up to a whole number of repeats. An eight-foot wall is 2.44 metres; in a paper repeating every 32cm that becomes eight whole repeats, or 2.56 metres.
Third, how many of those drops come off a roll — and only whole ones count. A 10.05 metre roll divided by a 2.56 metre drop is 3.9, and the 2.37 metres left over will not reach the ceiling. It is three drops a roll, which makes 26 drops into nine rolls.
The plain version of the same room gets four drops a roll and needs seven. Two whole rolls is what the pattern costs.
- Drops
- Strips of paper reaching floor to ceiling — the perimeter divided by the roll width.
- Roll width
- Usually 53cm in Europe, 68cm for many American rolls.
- Roll length
- Usually 10.05 metres. Check the label rather than assuming.
- Repeat
- How far up the paper the pattern starts again. Printed on the label.
- Cut length
- The height rounded up to a whole number of repeats, which is what each drop costs you.
A worked example
A twelve by ten foot room with eight-foot walls, in a standard 53cm roll with a 32cm straight-match repeat.
That works out to 9 rolls.
- Drops needed
- 26
- Cut length
- 2.56 m
- Drops per roll
- 3
- Wasted per drop
- 12.2 cm
- Wall perimeter
- 44.0 ft
Questions
How many rolls of wallpaper do I need for a 12 by 10 room?
Nine rolls for eight-foot walls in a standard 53cm roll with a 32cm repeat. The same room in a plain paper takes seven — the repeat costs two whole rolls.
Why not just divide the wall area by the roll area?
Because a roll only yields whole drops. The area maths says a 10.05 metre roll covers a certain number of square metres, but the last two metres of every roll is too short to reach the ceiling and is thrown away. Area arithmetic consistently comes out a roll or two short.
Should I deduct doors and windows?
No, and this deliberately does not. The offcuts go above and below the openings, so the paper you would have deducted is the paper that covers them. Deducting a standard door and window is a well-known way to end up short.
What is a pattern repeat?
How far up the roll you go before the pattern starts again. It is printed on the label, often as a number in centimetres beside a small symbol. A large repeat costs you more paper because every drop has to be cut to a whole number of repeats so the pattern lines up across the seams.
What is the difference between a straight match and an offset match?
On a straight match the pattern sits at the same height on both sides of a seam. On an offset — sometimes called a drop match — each drop is shifted half a repeat, so the design runs diagonally. An offset costs about half a repeat more per drop, which is why it can push you into another roll.
What is a free match?
A paper with no pattern to line up — plain, textured, or a random design like many grasscloths. Every drop is cut to the wall height and nothing is wasted on matching, which is why it needs the fewest rolls.
How many rolls should I buy spare?
At least one. Order everything in one go and check the batch number on every roll — colour shifts between print runs and a mismatched roll shows on the wall. Patterns are also discontinued regularly, so a roll bought a year later may not exist at all.
Does the calculation work for American rolls?
Yes — change the roll width and length. American wallpaper is often sold as a double roll about 68cm wide and 10 metres long, and single-roll pricing on a double-roll bolt confuses the count more than the maths does. Enter the dimensions of what physically arrives.
What if the drop is longer than the roll?
That happens on a stairwell or a double-height wall. There is nothing to divide, so it works out one roll per drop, which is expensive but correct. Check the roll length first — some papers are sold in longer rolls for exactly this.