What this calculator works out
Buying wallpaper comes down to three numbers a roll's own label can't answer: how many strips reach round the room, how many of those strips one roll gives you, and how many rolls that adds up to. This tool takes the total wall width you're papering, the wall height, a roll size and, if the paper has one, a pattern repeat, and turns those into strips, drops per roll and a rolls-to-buy figure, with the wastage shown honestly rather than hidden inside a padded estimate.
It handles both major roll conventions: the UK standard roll, 10.05m long and 53cm wide, and the American double roll, commonly 10m long and 27 inches (about 68.6cm) wide, plus a custom size for anything else a supplier stocks. Straight-match and drop-match (offset, half-drop) patterns are worked separately, since a drop match genuinely needs more paper for the same wall.
How the maths works
Everything starts with one drop, the length of paper cut for one strip of wall. That's never just the wall height: a 10cm trim allowance is standard trade practice, enough spare paper to line the drop up at the ceiling and trim it clean at the skirting board.
Once a pattern repeats, the usable drop has to be a whole multiple of the repeat, rounded up, so the design lines up at the same point on every strip: a 240cm wall with a 64cm repeat needs 4 repeats' worth of paper (256cm), not 3.9. Drop match adds a further half repeat on top of that, since the pattern is deliberately offset on alternate strips and every drop has to carry that offset through.
From there, drops per roll is the roll's length divided by the usable drop, rounded down, since a part-drop is offcut, not a usable strip. Strips needed is the total wall width divided by the roll's width, rounded up. Rolls to buy is strips divided by drops per roll, rounded up again.
Wastage is the gap between what those rolls actually contain and what the strips need. Plain paper on a straightforward wall wastes very little; a large repeat with a drop match can lose a quarter of every roll, which is why this page shows the figure rather than hiding it inside a rounder-sounding roll count.
A worked example
Take a bedroom wall totalling 14m once every wall is added together, 2.4m high, a plain UK-standard paper, no repeat. Usable drop: 240 + 10 = 250cm. One roll gives 1005 ÷ 250 = 4 drops. Strips needed: 1400 ÷ 53 = 26.42, rounded up to 27. Rolls to buy: 27 ÷ 4 = 6.75, rounded up to 7, holding 70.35m against the 67.5m the strips actually use, a touch over 4% wastage, about as tight as wallpaper buying gets.
Swap in a patterned paper with a 64cm repeat on the same wall and roll: the usable drop jumps to 256cm (4 repeats of 64cm), drops per roll falls to 3, and the same 27 strips now need 27 ÷ 3 = 9 rolls, two more than the plain paper, purely from the rounding-up at each stage stacking together. An American-market aside: the same plain wall in US double rolls (10m × 27in) needs 1400 ÷ 68.6 = 21 strips and 4 drops per roll, so 21 ÷ 4 = 5.25, rounded up to 6 rolls, at roughly 12.5% wastage.
Straight match versus drop match
A straight match lines the pattern up level: motif for motif, every strip repeats at exactly the same height as its neighbour. A drop match, also called an offset or half-drop match, deliberately staggers the design, so the motif on one strip sits half a repeat lower than the strip beside it, the way a diamond or brick-style pattern often does. That only matters for buying because a drop match needs the extra half-repeat allowance on every drop. A paper's listing or sample book states which type it is, next to the repeat measurement.
Doors, windows and when to actually subtract them
It's tempting to subtract every door and window from the wall width, and most first-time calculations overcorrect by doing exactly that. Decorators generally advise against it for ordinary doors and windows: full-height strips are still needed above, below and beside most openings, and any offcut from trimming round a frame rarely stretches to cover anywhere else. The exception is a genuinely large opening that runs floor to ceiling, a patio door or picture window: no paper hangs there at all, so its width is worth taking out, which is what the "large openings" field above is for, kept separate so the default stays the conservative one.
Batch numbers and dye lots
Wallpaper is printed in production runs called batches or dye lots, and even the same product code can shift subtly in colour between them. Buying every roll in one order, and checking the batch number on each label matches before hanging any of them, avoids a visible seam of mismatched colour across a wall. It's also why the headline figure here always includes one spare roll, kept flat and out of direct sunlight so a repair years later still draws on paper from the original batch.
Lining paper
Some walls need a plain lining paper hung first, at right angles to the way the top paper will run. It's the usual fix for a wall with a slightly rough, uneven or previously painted surface, giving the top paper a smooth surface to bond to. Lining paper is measured the same way, just run this calculator again with the lining roll's own size and a repeat of zero.
Questions people ask
Do I need to subtract doors and windows from the total?
Not for an ordinary door or window: full-height strips are still needed around it, and the offcuts rarely stretch to cover anything else. Only a genuinely large opening that runs floor to ceiling, a patio door or picture window, is worth subtracting, using the "large openings" field above.
What's the difference between straight match and drop match?
Straight match lines the pattern up level across every strip. Drop (or offset, half-drop) match deliberately staggers it by half a repeat on alternate strips, which needs roughly half a repeat's extra paper on every drop, so it uses more paper for the same wall.
Why does the answer always include one extra roll?
Wallpaper is printed in batches (dye lots), and colour can shift subtly between them. One spare roll from the same order, stored flat, means a future repair can still draw on paper from the original batch rather than a replacement that may not quite match.
What is a pattern repeat, and what does 0 mean?
It's the vertical distance before a patterned design repeats itself down the roll, printed on the paper's label or product page. A repeat of 0 means a plain paper, a texture, or any design with no visible repeat to match, so the usable drop is simply the wall height plus the trim allowance.
Should I use lining paper first?
It's the standard fix for a wall that's slightly uneven or was previously painted, since it gives the top paper a smooth, consistent surface and stops small imperfections showing through. Lining paper is measured the same way, just run this calculator again with the lining roll's own size and a repeat of zero.
Why do UK and US rolls give such different roll counts for the same wall?
The US double roll is wider (27in/68.6cm against the UK's 53cm) but a touch shorter (10m against 10.05m), so it needs fewer, wider strips for the same wall width, but the last drop of most rolls tends to leave a bit more length unused. Neither is "wrong"; they're just two different regional conventions for how a roll is cut.
This calculator applies the standard trade method, whole drops per roll and a fixed trim allowance, to the measurements and roll size you enter. Real walls have corners, alcoves and the odd out-of-true ceiling line that a plain width-and-height figure can't capture; measure carefully and treat the result as a solid ordering estimate rather than the final word for an unusual room.