How does the wallpaper calculator count rolls?

It works in strips, not area. It divides the wall run by the roll width to get how many vertical strips you need, then divides the roll length by each strip's cut length to get how many strips one roll yields. Strips needed divided by strips per roll, plus a waste percentage, rounded up, is the number of rolls.

Why use strips instead of just dividing the areas?

Wallpaper can only be hung in full-width vertical strips, so there is always offcut waste at the top and bottom of each drop. Dividing total area by roll area ignores this and under-estimates, which is why trade calculators count whole strips per roll instead.

What is a pattern repeat and why does it matter?

The pattern repeat is the vertical distance before the design starts again. On a patterned paper every strip must be cut to a whole number of repeats so the design lines up wall-to-wall, which lengthens each cut and means fewer strips come from each roll. Plain or free-match papers have no repeat to line up.

What is the difference between a straight match and a drop match?

On a straight (or set) match the pattern lines up at the same height on every strip. On a drop (offset) match, alternate strips are shifted by half a repeat, so the design steps diagonally across the wall. Both round each strip up to a whole repeat in this tool, so a large repeat noticeably increases the rolls needed.

How much waste should I allow?

Around 10% is a sensible default and the tool's starting value. Add more — 15% or higher — for big or busy patterns, rooms with many corners, or if you want extra for future repairs. Always buy whole rolls from the same batch number so the colour matches exactly.

Does the calculator deduct doors and windows?

No, by design. The short offcuts you save above and below an opening rarely add up to a whole roll, and the spare is useful for mistakes and later patching. Leaving openings in keeps the estimate safely on the buy-enough side.

Wallpaper Calculator

A wallpaper calculator that tells you how many rolls to buy for a room — and roughly what it will cost — from your wall measurements, the roll size on the label and the paper’s pattern repeat. Unlike a simple area-divided-by-area sum, it works the way a decorator actually hangs paper: in full-width vertical strips, accounting for the offcut waste at the top and bottom of every drop and the extra length a patterned paper needs so the design lines up across the wall. It works in metric or imperial and is handy whether you are doing a single feature wall or a whole room.

How it works

First the tool figures out the cut length of one strip: the wall height plus a trim allowance for slack at the top and bottom. For a patterned paper it then rounds that cut up to a whole pattern repeat, because every strip has to start at the same point in the design to match its neighbours. Next it counts how many of those strips come out of a single roll, and how many strips wide your walls are:

cut length     = wall height + trim, rounded up to a whole repeat
strips/roll    = floor(roll length / cut length)
strips needed  = ceil(total wall run / roll width)
rolls          = ceil( strips needed / strips per roll × (1 + waste) )

Strips needed is always rounded up, because you cannot hang a fraction of a strip. The waste percentage then adds a safety margin for trimming, corners and repairs before the final round-up. A free-match paper skips the repeat step entirely, so its strips are shorter and more come from each roll.

Worked example

Take a room with a 5 m total wall run and 2.4 m ceilings, papered with a standard euro roll: 53 cm wide and 10 m long, with a 32 cm straight pattern repeat, a 10 cm trim allowance and 10% waste.

Strip cut length: 2.4 m + 0.10 m = 2.50 m, rounded up to a whole 32 cm repeat gives 2.56 m per strip.
Strips per roll: 10 m ÷ 2.56 m = 3 full strips from each roll.
Strips needed across: 5 m ÷ 0.53 m = 9.43, rounded up to 10 strips.
Rolls before waste: 10 ÷ 3 = 3.33 rolls; add 10% and round up to 4 rolls.

At £25 a roll that is an estimated £100. Switch the same paper to a free match and each strip drops to 2.50 m, so four still come from a roll and the total can fall to three rolls — which is exactly why the pattern repeat is worth entering accurately.

Reference — roll sizes and repeats

A standard European wallpaper roll is 53 cm × 10 m (about 5.3 m² of usable paper). American rolls are commonly sold “double” at roughly 68.5 cm × 8.2 m. Pattern repeats range from 0 cm on plain papers to 64 cm or more on large botanical or geometric prints — always read the actual figures from the label, as they vary by brand. The trim allowance covers the few centimetres you lose squaring up the top and trimming at the skirting; 10 cm is typical. Remember that the result is a minimum — buy whole rolls, keep them from the same batch number, and treat the spare as insurance.

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