Wallpaper Calculator — Rolls by Drop, Not by Area
Most wallpaper calculators divide area by roll size and get it wrong, because the pattern repeat wastes paper at the top of every drop. This one counts drops the way a decorator does.
Take this list to the store
We'll email the quantities above, what you typed in, and a link that reopens this calculator already filled in — so you can adjust it on your phone in the aisle.
How to work it out
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Measure the room, not the wall
Enter the floor length and width and the perimeter is worked out for you. Doing one accent wall? Enter that wall's width as the length and put a very small number in the width — or simply divide the strip count yourself.
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Find the pattern repeat on the label
Every roll states it, usually in inches. This is the single number that decides how much paper you waste, and the one that area-based calculators ignore. A plain paper has no repeat; large florals can repeat every 25 inches.
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Cut every drop to a whole repeat
To make the pattern line up, each strip has to start at the same point in the design. That means cutting every drop to the next whole multiple of the repeat, and throwing away the difference. The calculator shows you both the cut length and what it costs you.
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Buy all the rolls in one batch
Check the batch or run number on every roll — color shifts between batches and it is obvious on a wall. Buy one extra roll while the batch is available; returning an unopened roll is usually easier than matching one later.
Drops you get from a US double roll
A US double roll is 27 in. wide by 27 ft long. Height includes 4 in. of trim allowance.
| Wall height | Pattern repeat | Cut each drop | Drops per roll | Paper used |
|---|---|---|---|---|
| 8 ft | None | 96 in. | 3 | 6.8 ft |
| 8 ft | 12 in. | 108 in. | 3 | 6.8 ft |
| 8 ft | 21 in. | 117 in. | 2 | 4.5 ft |
| 9 ft | None | 108 in. | 3 | 6.8 ft |
| 9 ft | 12 in. | 120 in. | 2 | 4.5 ft |
| 9 ft | 21 in. | 129 in. | 2 | 4.5 ft |
| 10 ft | None | 120 in. | 2 | 4.5 ft |
| 10 ft | 21 in. | 141 in. | 2 | 4.5 ft |
Notice the jump: at a 9 ft wall, a 21 in. repeat costs you a whole drop per roll compared with a plain paper.
Roll sizes you will meet
| Type | Width | Length | Covers (plain paper) |
|---|---|---|---|
| US double roll | 27 in. | 27 ft | About 56 sq ft |
| US single roll | 27 in. | 13.5 ft | About 28 sq ft |
| European roll | 20.5 in. | 33 ft | About 56 sq ft |
| Peel and stick | 24–26 in. | Varies | Sold by the panel or foot |
US paper is often priced by the single roll but only sold in doubles. Check which you are being quoted.
Why area-based wallpaper calculators come up short
Divide your wall area by the 56 sq ft printed on the roll and you will be one or two rolls short on anything with a pattern. The roll does contain 56 sq ft of paper — but you cannot use all of it.
On a 9 ft wall with a 21 in. repeat, each drop must be cut at 126 in. rather than the 112 in. you actually need, because 126 is the next whole multiple of 21. That is 14 inches binned from every single strip. Across a room it adds up to most of a roll.
How many rolls for an accent wall?
Measure the wall's width in inches and divide by the roll width — 27 in. for US paper. A 12 ft wall is 144 in. wide, so 144 ÷ 27 = 5.3, meaning 6 drops. With a 9 ft ceiling and a 21 in. repeat you get 2 drops per roll, so you need 3 rolls.
Straight match, half-drop, or random
- Random match — textures, grasscloth, plain. No alignment, almost no waste. Reverse alternate strips to even out shading.
- Straight match — the pattern lines up straight across at the same height on every strip. Waste is one repeat per drop.
- Half-drop match — alternate strips sit half a repeat lower, giving a diagonal effect. Beautiful, and the most wasteful: budget an extra half repeat per drop, which the calculator does for you.
Order one more roll than you need
Wallpaper is the material where running out hurts most. A mis-cut drop, a torn corner, or a batch that sells out mid-job all cost far more than one spare roll. Keep the cut-offs too — a patch cut from the same batch is invisible, one from a new batch never is.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
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perimeter = 2 × (length + width), summed over every sectionThe run of wall the drops have to cover. -
drop length = wall height + 4 in. trimTwo inches top and bottom, because ceilings and floors are rarely level. -
cut length = next whole multiple of the pattern repeatEvery strip must start at the same point in the design, so the excess is binned. -
half-drop match uses 1.5 × the repeatAlternate strips sit half a repeat lower, wasting more. -
strips = (perimeter − openings) ÷ roll width, rounded upA door removes about one strip's width, a window about half. -
drops per roll = roll length ÷ cut length, rounded downYou cannot use a partial drop, so this always rounds down. -
rolls = strips ÷ drops per roll, rounded upThis is the step area-based calculators skip, and why they come up short.
Common questions
How many rolls of wallpaper do I need for a 12x12 room?
The perimeter is 48 ft, or 576 in. Take off about 27 in. for a door and 13.5 in. for a window, divide by the 27 in. roll width, and that is 20 drops. With a 9 ft ceiling and a 21 in. repeat each drop cuts at 126 in., so you get 2 drops per roll — 10 rolls. A plain paper with no repeat gets 3 drops per roll, so only 7.
What is a pattern repeat?
The vertical distance before the design starts again. It is printed on the roll label. Every strip has to be cut so the pattern starts at the same point, so the repeat is the amount of paper you throw away at the top of each drop.
What is the difference between a single and double roll?
A double roll is one continuous roll with twice the paper — 27 ft rather than 13.5. US wallpaper is usually priced per single roll but only sold in doubles, which catches people out. A double roll gives you more usable drops, because fewer are lost to the ends.
Should I deduct doors and windows?
Only roughly. A door is about one drop's width and a window half, which is how this calculator treats them. Never deduct the exact area — you still need a full-height drop above and below a window, cut from a fresh piece.
How much extra should I allow for trimming?
Four inches per drop — two at the top and two at the bottom. That is built into the cut length shown above. Ceilings and floors are rarely level, and that margin is what lets you slide a drop to meet them.
Does peel-and-stick wallpaper work the same way?
The drop counting is the same, but roll sizes vary much more and many are sold by the panel. Check the stated width and length against the roll options above, and expect the same repeat waste on any patterned design.
Can I paper over existing wallpaper?
It is not advisable. The new paste soaks the old paper and both come away together, usually taking some drywall face with them. Strip it, size the wall, and you will get a far better result.
What if my ceiling is not level?
Work to the ceiling rather than the floor, since that is the line the eye follows. Baseboard hides a lot at the bottom. The 4 in. trim allowance in the cut length gives you room to adjust as you go.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- Wallcoverings Association (WA) measuring guidance — the drop method and trim allowance
- Roll specification labels — width, length, pattern repeat and match type
- ASTM F793 — wallcovering categories and performance classes
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 11, 2026.