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Wallpaper Calculator

Calculators · Added

Wallpaper is not bought by area, and calculating it that way is what leaves people a roll short on the last wall. This counts drops — full-height strips the width of the roll — rounds each cut up to a whole pattern repeat, and works out how many drops a roll actually yields. Enter the room, the roll size from the label and the repeat, and it shows the working rather than just a number.

m
m
m
cm
m
Pattern match

No alignment needed — plain papers and random textures

cm

From the label. Zero for a plain paper.

cm

Top and bottom together. 10 cm is usual.

m

From the same batch

Leave blank to skip the cost

How to use the wallpaper calculator

  1. 1Enter the room's length and width, or the perimeter of the walls being papered, with the ceiling height.
  2. 2Set the roll width and length from the label, or pick a standard size.
  3. 3Enter the pattern repeat and choose the match type — free, straight or offset.
  4. 4Read the number of rolls, and check the drops-per-roll figure to see where the waste is going.

Examples

A plain paper in a 4 × 4 m room

Input
16 m perimeter, 2.4 m ceilings, 53 cm × 10.05 m rolls, no repeat
Result
30 drops at 2.50 m, 4 drops per roll, so 8 rolls plus a spare

The same room in a paper with a 64 cm repeat

Input
Straight match, 64 cm repeat
Result
Each cut rounds up to 2.56 m, so 3 drops per roll instead of 4 — 10 rolls, two more than the plain paper

Identical roll dimensions, identical room, two extra rolls. That is what the repeat costs.

A door in the wall

Input
One 0.9 m door, deduction switched on
Result
One whole drop deducted — a door is full height and wide enough to skip a strip

About the wallpaper calculator

Drops, not square metres

The unit that matters in papering is the drop: one full-height strip, exactly as wide as the roll. A wall 4.1 m wide takes eight drops of 53 cm paper, not 7.74 — the ninth part-width is a cut piece off a ninth drop, and the rest of that drop is waste.

The same happens at the roll. A 10.05 m roll cut into 2.5 m drops gives four with 0.05 m left; cut into 2.56 m drops after a repeat is allowed for, it gives three with 2.37 m left, which is nearly a whole drop of paper thrown away. That second rounding is the one people never see coming, and it is why a few centimetres of repeat can cost two rolls.

Where the trim allowance goes

The default here is 10 cm per drop, a few centimetres at each end. It exists because ceilings and skirtings are not level and floors are not flat: the paper is hung slightly long and trimmed in place against whatever line the room actually has.

It is worth measuring the height in several places rather than once. In an older house the difference across a single wall can be two or three centimetres, and the allowance has to cover the worst of it, not the average. If your ceilings really are level, reducing the allowance sometimes gets an extra drop out of every roll — the tool says so when it would.

What this cannot know

It assumes flat, rectangular walls papered from floor to ceiling. Sloping ceilings, chimney breasts, dormers, stairwells and anything papered horizontally all change the arithmetic, usually upwards, and a stairwell in particular is a job where the longest drop rather than the average one sets the roll count.

It also cannot see the room. Whether the pattern is centred on the chimney breast, which corner the papering starts from and where the inevitable mismatch is hidden are decisions that change how many drops get cut, and they are made standing in the room with a plumb line.

Frequently asked questions

Why not just divide the wall area by the roll area?
Because two roundings sit between them and area arithmetic sees neither. You cannot hang three-quarters of a strip, so the drops for each wall round up; and a roll yields a whole number of cuts with the remainder wasted, so the rolls round up too. On a typical room the area method comes out one to two rolls short, and it is short in exactly the situation where buying more later means a different print batch.
How does the pattern repeat change the answer?
Every drop has to start at the same point in the pattern or the join will not match, so each cut is rounded up to a whole number of repeats. A 2.4 m wall in a paper with a 64 cm repeat needs a 2.56 m cut, wasting 16 cm on every drop before trimming. It is why the repeat is printed on the label, and why it is often the single largest cost in a wallpaper order.
What is an offset or half-drop match?
A pattern where alternate drops are shifted by half a repeat, so the design steps diagonally across the wall rather than running in horizontal bands. It looks better and wastes more: the usual trade allowance is an extra half repeat per drop, which is what this applies. A straight match aligns every drop at the same height, and a free match — plain papers, random textures — needs no alignment at all.
Why are windows not deducted?
Because the short pieces above and below a window still have to line up with the full drops either side, so they usually have to be cut from fresh paper rather than from the offcut of another wall. Deducting a window's area is the classic way to end up short. Doors are different — a door is normally full height and wide enough to skip a whole drop — so they are deducted, and you can switch that off.
Why buy a spare roll?
Wallpaper is printed in batches, and colour varies measurably between them. A roll bought six months later may be a visibly different shade, which on a feature wall is the whole wall. One spare roll from the same batch, kept in a cupboard, is far cheaper than re-papering after a knock or a leak.

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