How many rolls of wallpaper do I need?
For a standard 10 ft by 12 ft room with 8 ft ceilings, one door, and one window, you need about 6 to 8 single rolls of non-patterned paper and 8 to 10 rolls of paper with a 12 in half-drop match. The exact number depends on four things: the actual square footage of each wall, the size of the openings you can subtract, the pattern repeat and match type, and how much waste you build in for trimming. Rollsy calculates all four in the browser and prints a shopping list you can take to the store.
You can run the math at appcrib.com/rollsy. It is free, there is no sign-up, and no account is stored.
Why most wallpaper calculators get the number wrong
Most of the free calculators online pick one of three things to do well and drop the other two. Omni Calculator gets pattern repeat and door and window deduction right, but there is no print output. VizualizeAI nails per-wall entry and match type selection, but there is no export you can take to the store. Turn2Engineering has a PDF and the most rigorous math, but there is no per-wall entry and no opening deduction. Retailer tools, the ones bolted to Lowe's and WallpaperDirect, tend to push you toward a product rather than toward an accurate count.
The result is that the typical DIY buyer over-orders by 20 to 30 percent. That is a full extra roll per bathroom, sometimes two for a feature wall. Rollsy does all three: per-wall entry with opening deduction, match-type selection that handles half-drop correctly, and a print-ready shopping list with a batch and dye lot reminder.
How do I calculate wallpaper with a pattern repeat?
The pattern repeat is the vertical distance between the start of one motif and the start of the next. When you hang a strip of paper, each drop has to start on a whole repeat so the pattern lines up with the strip next to it, which means your effective drop height is always rounded up to the next repeat.
For a straight match, the math is:
adjusted_drop_height = ceil(wall_height / pattern_repeat) * pattern_repeatIf your wall is 96 inches tall and the repeat is 18 inches, every drop has to be cut at 108 inches, not 96. That extra 12 inches per drop is real waste, and it is the number one reason buyers come up short.
For a half-drop match, every other drop starts at the half-repeat, which shifts the pattern diagonally across the wall. The effective drop height is still rounded to the repeat, but you lose an additional half-repeat's worth of paper on every second strip. The Turn2Engineering worked examples are a good sanity check. Rollsy's unit tests use them directly.
What is the difference between straight match and half-drop match?
Straight match patterns line up horizontally. Every drop starts at the same spot in the repeat, so cuts of equal length tile cleanly side by side. Half-drop match patterns shift the design down by half the repeat on every other strip, which creates the diagonal, quilt-like look of most traditional florals and damasks. The trade-off is waste: half-drop patterns use more paper because the offset means you cannot always start a fresh strip at a convenient place in the repeat.
A third option, usually labeled no match or random match, means the pattern has no regular alignment, often because it is a texture or a free-form print. In that case the calculator can ignore the repeat entirely and use the raw wall height as the drop.
Rollsy asks for match type as a single chip selection (no match, straight, half-drop) and applies the right formula automatically. You do not need to know the math to get the right number, but the breakdown panel shows every step so you can check it yourself.
Should I subtract doors and windows when calculating wallpaper?
Yes, with one asterisk. A standard interior door is 80 in by 32 in, which is about 17.8 square feet. A typical bedroom window is 36 in by 48 in, or 12 square feet. Between the two, a room with one door and two windows can give back close to 42 square feet of wall area, which at common drop heights is most of a single roll. Ignoring openings is why retailer tools over-order.
The asterisk: you still want to keep the cut pieces above and below the opening, because you may need them to patch a mistake or fill a tight area near a baseboard. The deduction in the math is fine. The material left over lives in your closet until the job is done.
Rollsy lets you add up to six openings per wall with editable dimensions. Each wall tracks its own openings so you do not have to average across the room.
How much wallpaper do I need to account for waste?
The standard recommendation is 10 percent for plain or small-repeat paper, 15 percent for straight match, and 15 to 20 percent for half-drop match or any large-repeat design. You can push it lower if you are a confident hanger with a simple pattern, or higher if the pattern has long repeats (some botanicals and murals run 25 inches or more, which means every cut leaves a big offcut).
The reason for the buffer is not the cut itself. It is the batch. Wallpaper is printed in batches, and the color on one batch does not quite match the color on the next. If you run short mid-project and go back for another roll, the new roll may come from a different dye lot. The seam will show. Buying the extra up front, from the same batch, is cheaper than re-doing the wall.
Rollsy defaults the waste slider to 10 percent and lets you push it between 0 and 30. The final roll count is rounded up from the raw count with the waste added, so the number on screen is the number you buy.
What is a single roll vs a double roll?
In the US, wallpaper is priced as a single roll but almost always sold as a double roll. A single roll in the US is 20.5 in wide by 33 ft long, or 56 square feet. A double roll is 27 in wide by 27 ft long, also 56 square feet, but sold as one physical bolt that you cut into two drops. In Europe, the standard roll is 53 cm wide by 10.05 m long.
The math works out the same if you enter the actual width and length of the roll you are buying. Rollsy has imperial defaults pre-filled at the US single-roll spec (20.5 in by 33 ft) and metric defaults at 53 cm by 10.05 m. If your retailer ships a double roll, enter 27 in by 27 ft. The calculation is not locked to a retailer.
What Rollsy does that the other tools do not
Rollsy prints a shopping list. When the roll count is good, you click Print Shopping List and your browser opens a print view with the final count, the roll spec you used, the pattern repeat, the match type, a blank write-in for the pattern name and SKU, a blank write-in for the batch or dye lot, and a reminder to buy all rolls from the same batch. The ads and the nav are hidden. It fits on a single page in US Letter or A4.
You take it to the store. You fill in the SKU at the shelf. You confirm the batch number with the cashier. You buy enough paper, from one batch, on one trip.
That is the whole job.
Open Rollsy. Enter your walls, your pattern, your roll. Print your list. Go.