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Wallpaper Calculator Guide
Rolls from your wall area, with the pattern repeat accounted for — because the repeat is what actually decides how many you need.
Wall area = perimeter × height − openings
A 12×14ft room at 9ft high with a door and two windows ≈ 417 sq ft.
At ~50 sq ft usable per roll that's 9 rolls — but a large pattern repeat can push it to 11.
The Repeat Is the Hidden Cost
A plain paper wastes almost nothing. A paper with an 18in repeat can waste 20% or more, because every strip has to start at the same point in the pattern.
You cut a strip, and up to a full repeat length goes in the bin so the next one lines up. On a 9ft wall with an 18in repeat, that's up to 18in wasted per strip — and there are a lot of strips.
Buy It All at Once, From One Batch
Wallpaper is printed in batches, and batches differ. Not by much — but enough to see a line down your wall in daylight where one batch meets another.
Check the batch number on every roll before you leave, and buy one extra. Coming back in six weeks for one more roll usually means a different batch, and the difference will be visible exactly where you don't want it.
Don't Deduct Small Openings
It's tempting to subtract every window precisely. Don't. You still have to paper around them, and the offcuts from a window reveal are rarely usable elsewhere.
This calculator deducts doors and windows at conservative sizes for that reason. Deduct aggressively and you'll be short — and being short is much worse than having a spare roll, because of the batch problem above.
Double Rolls and Single Rolls
American wallpaper is priced by the single roll but almost always sold as a double roll. The coverage figure that matters is what's in the package you actually carry out.
European rolls are a different size again — typically 10.05m by 0.53m, about 57 sq ft. Read the label rather than assuming; the numbers are close enough to be confusing and different enough to leave you a roll short.
Walls Are Never Plumb
Don't hang your first strip against a corner and assume it's vertical — it isn't. Strike a plumb line and work from that, or the pattern will visibly drift as you go round the room and there's no fixing it afterwards.
Related: carpet calculator, drywall calculator, crown molding calculator.
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