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Wallpaper Calculator
Rolls needed, accounting for the pattern repeat.
What it does. Rolls are calculated by drops, not by area. Divide the wall width by the roll width to get the number of drops, work out how many drops come from one roll after allowing for the pattern repeat, then divide. The repeat is what turns a simple sum into a real one.
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How to use Wallpaper Calculator
- Enter wall dimensions and ceiling height.
- Enter the roll size and pattern repeat from the label.
- Read drops per roll and the total rolls.
Why area is the wrong approach
Wallpaper is hung in full-height strips called drops. A drop that is 20cm short is useless — you cannot join a piece on — so the usable output of a roll is a whole number of drops with the remainder wasted.
A 10m roll and a 2.4m ceiling gives four drops and 0.4m of waste, even before pattern matching.
That is why area-based estimates run short. They implicitly assume you can use every square metre, and drops do not work that way.
The pattern repeat
| Repeat type | What it means | Extra waste |
|---|---|---|
| Free match / plain | No alignment needed | Minimal |
| Straight match | Pattern aligns across at the same height | Up to one repeat per drop |
| Offset / drop match | Alternate drops shift by half a repeat | Up to one repeat per drop |
| Large repeat (64cm+) | Common in florals and damask | Can cost a whole roll |
With a straight or offset match, each drop must be cut at the right point in the pattern, so the effective drop length is the wall height rounded up to the next whole repeat. A 2.4m wall with a 64cm repeat needs 2.56m per drop — 16cm wasted on every single drop.
Buy the rolls together
Wallpaper is printed in batches, and batch numbers matter more than with paint. Shade differences between batches are common and obvious once two drops hang side by side.
The batch number is printed on the label; check every roll matches before you start.
Buy one spare roll and keep the label. It costs less than discovering mid-wall that the shop has moved to a new batch, and it covers a future repair.
Frequently asked questions
How many rolls of wallpaper do I need?
Work in drops, not area. Divide wall width by roll width for the number of drops, work out how many full drops a roll yields after the pattern repeat, then divide. Area-based estimates run short.
How does the pattern repeat affect how much I need?
With a straight or offset match, each drop is cut to a whole number of repeats. A 2.4m wall with a 64cm repeat needs 2.56m per drop — 16cm wasted on every drop, which can cost a whole roll.
What is the difference between straight and offset match?
Straight match aligns the pattern across at the same height on every drop. Offset shifts alternate drops by half a repeat. Both need cutting to whole repeats; offset often wastes slightly less.
Why do batch numbers matter?
Wallpaper is printed in batches and shade differences between them are common and obvious once two drops hang side by side. Check every roll carries the same batch number before starting.
Should I subtract doors and windows?
Only for full-height openings like patio doors. A window mid-wall still needs drops above and below it, and the offcuts rarely align, so deducting its area overestimates the saving.