Wallpaper Calculator - Rolls, Pattern Repeat & Cost

How to use it

1. Pick the mode. Room takes a length, a width and a ceiling height and builds the four walls for you. Wall list lets you name each wall and give it its own width and height, which is the right choice for a feature wall, a chimney breast or a room that is not a rectangle. Panels is for peel and stick products sold as a panel set rather than a roll.
2. Measure and enter the walls in feet and inches. Measure the wall itself rather than a floor plan, and measure the ceiling height at three points across the room: an out of level ceiling is normal, and the tallest reading is the one that decides your cut length.
3. Count the doors and windows. By default they do not shorten the run, because paper hangs straight past an opening and gets cut out afterwards, which keeps a seam away from the corner where tears start. Turn the deduction on only if you plan to piece around the opening. A cased opening, a wall of glass or a fireplace breast goes in the large opening field, and it only comes off the run once it spans 80 percent of the wall height.
4. Set the roll format. This is the trap feature. US paper is priced per single roll and shipped as a double roll bolt, so choose the format the seller will actually ship: 20.5 in by 33 ft is the standard American double roll, 27 in by 27 ft is the wide double, and the two single roll presets are half of each. A euro roll of 52 cm by 10.05 m is the same coverage as a US double. Pick Custom and type the width and length off your own roll label if none of them match.
5. Enter the pattern repeat and the match type from the label. Repeat is the vertical distance before the design starts again. Random or free match means no alignment at all, straight match lines up level across the seam, and half drop means alternate strips start half a repeat further down the roll. If the label says 0 in of repeat, choose random.
6. Check the trim allowance. Four inches total, two at the top and two at the bottom, is the working default and it is what absorbs an out of level ceiling. Selvedge or overlap stays at 0 for modern pre-trimmed paper and goes to about 0.5 in for an untrimmed or hand printed paper that you butt with an overlap.
7. Read the answer. The headline is the roll count in your chosen unit with the single roll equivalent under it, and the two drawings show the same thing two ways: the wall with its numbered strips, and one roll with the drops marked off along it and the leftover hatched.
8. Compare wall by wall against a continuous run. Both are always computed. Wall by wall is the safer real world number because each wall starts a fresh strip and the offcut at each corner is scrap. Continuous is what you get if you wrap strips around internal corners, which usually saves a roll.
9. Look at the five format comparison below the tool. It runs the same job through every standard roll format, so you can see what a wider paper or a longer bolt does to the roll count and the waste before you commit to a product.
10. Put your own prices in the ledger. The roll price, the primer or sizing, the adhesive for unpasted paper and an optional install labor line are all editable, and every one of them is a planning number rather than a quote.

At a glance

• 12 x 12 room, 8 ft ceiling, straight match, 21 in repeat: 48 ft of wall run, 384 sq ft. Each drop cuts at 8 ft 9 in, three drops come off a 33 ft roll, and 32 strips need 11 double rolls, or 10 if you hang in a continuous run. That is 22 single rolls and 121 linear yards. The area method would have told you 8.
• One 12 ft feature wall, 8 ft ceiling, same paper: 8 strips at 8 ft 9 in each. Three drops per roll, so 3 double rolls plus a spare, 15 ft 6 in of remnant left on the last one and about 20 percent cutting waste. Two rolls would leave you two strips short of the corner.
• Peel and stick mural, 10 ft wall, 24 in panels sold in pairs: Panels overlap 1 in so each covers 23 in, which is 6 panels and 3 sets. Nine foot panels leave 12 in to trim on an 8 ft wall, and the set waste is 26 percent. About $150 at $50 a set.

How the math works

Every figure on this page comes from the strip method, and every step of it is an answer to the same wrong shortcut. The area method says a standard roll covers about 56 sq ft, so divide your wall area by 56 and add 10 percent. That fails because wallpaper is not sold by the square foot in any way you can spend: it is sold in a fixed length, and a wall is covered by whole vertical drops cut from that length. Start with the usable width, which is the roll width minus any overlap, 20.5 in on a standard US roll. Strips are the wall run divided by that usable width and rounded up, per wall for the safe number and across the whole run for the continuous one, so a 12 ft wall takes ceil(144 / 20.5) = 8 strips and a 48 ft room perimeter takes 29 in one run but 32 wall by wall. Next the cut length. The base drop is the ceiling height plus the trim allowance, 96 + 4 = 100 in on an 8 ft wall. On a matched paper that gets rounded up to a whole pattern repeat, because you can only cut where the pattern allows: ceil(100 / 21) x 21 = 105 in, so five inches of pattern waste on every strip before you have hung anything. Then the line that decides the order. Strips per roll is floor(roll length / cut length), so a 33 ft roll cut into 8 ft 9 in drops gives floor(396 / 105) = 3 drops, not 3.77, and the remaining 81 in is not long enough for a fourth. A half drop match is charged differently, because every strip after the first has to advance half a repeat down the roll before the pattern lines up, which makes it floor((roll + repeat/2) / (cut + repeat/2)). On a 10 ft 5 in drop and a 25 in repeat that is the difference between three drops a roll and two, and on a 12 by 12 room it is the difference between 11 rolls and 16. Rolls are ceil(strips / strips per roll), plus one spare if you want repair stock from the same dye lot. If the cut length is longer than the roll, strips per roll is zero and this page says so out loud instead of returning a huge number, because that paper genuinely cannot hang on that wall in one piece. Waste is reported twice because there are two kinds. Cutting waste is the paper you take off the rolls against the paper that ends up on the wall, which is where the trade's 10 to 15 percent for a straight match and 20 to 25 percent for a half drop belong. Total waste adds the remnant left unused on every roll, which is why a small accent wall can show 40 percent while a whole room shows 30. Cost is each quantity at a price you type in: rolls, primer or sizing at about a gallon per 350 sq ft, adhesive at about a gallon per five double rolls for unpasted paper, and an optional labor line per roll. Peel and stick uses a different chain entirely: panels are ceil(wall width / (panel width minus overlap)), sets are ceil(panels / panels per set), and the panel height is checked against the wall height, because a horizontal join across a peel and stick wall is very hard to hide.

1. 1. Measure the run and the height, and measure the height twice

   The run is the horizontal distance the paper has to cover: one wall in wall list mode, the perimeter in room mode, so a 12 by 12 room is 2 x (12 + 12) = 48 ft. The height is floor to ceiling at the tallest point. Measure it at three places across the room, because ceilings are rarely level and the tallest reading is the one that sets the cut length for every strip. Getting this wrong by an inch on a patterned paper can push every drop up a whole repeat, which on a 25 in repeat costs 25 in of paper 32 times over.

2. 2. Turn the run into a strip count, not a square footage

   Usable width is the roll width minus any overlap, so 20.5 in for a standard US roll with modern pre-trimmed edges. Strips are the run divided by that and rounded up. A 12 ft wall is 144 / 20.5 = 7.02, so 8 strips, and the eighth one is a 3.5 in sliver in the corner. Do this wall by wall rather than across the whole perimeter, because each corner forces a fresh strip and the offcut is scrap. The tool computes the continuous number too, and the difference between them, usually one roll, is exactly the value of wrapping strips around internal corners.

3. 3. Add the trim, then round the drop up to a whole repeat

   Base drop is the height plus the trim allowance, 96 + 4 = 100 in on an 8 ft wall. On a random or free match that is your cut length and you are done. On a straight or half drop match you can only cut where the pattern allows, so it rounds up to a whole repeat: ceil(100 / 21) x 21 = 105 in. An 8 ft 8 in drop on a 28 in repeat rounds to 9 ft 4 in. That rounding is pure pattern waste on every single strip, and it is the reason two papers that cover the same square footage can need a different number of rolls.

4. 4. Count the drops that fit on one roll, and floor the answer

   This is the step nothing else on page one performs. Strips per roll is floor(roll length / cut length). A 33 ft roll is 396 in, and at a 105 in cut length that is 396 / 105 = 3.77, which floors to 3. The remaining 81 in cannot make a fourth drop, so it is remnant. Say that number out loud when you are comparing papers: a drop of 8 ft 3 in would still give 3 drops a roll, but a drop of 8 ft 6 in on a 24 in repeat cuts at 8 ft 8 in and still gives 3, while a 9 ft ceiling on a 25 in repeat cuts at 10 ft 5 in and gives 3 by 21 inches. The margin is often that thin.

5. 5. Charge a half drop match for the offset it costs

   On a half drop, alternate strips start half a repeat further down the roll, so every strip after the first on a roll costs an extra repeat/2 of length. Capacity becomes floor((roll length + repeat/2) / (cut length + repeat/2)). On a 33 ft roll with a 10 ft 5 in drop and a 25 in repeat: a straight match gives floor(396 / 125) = 3, a half drop gives floor(408.5 / 137.5) = 2. Same paper, same wall, one third fewer drops per roll. On a 12 by 12 room with 9 ft ceilings that is 16 rolls instead of 11, about $275 of paper, decided entirely by a word on the label.

6. 6. Divide, round up, and add a spare from the same dye lot

   Rolls are ceil(strips / strips per roll): 32 strips at 3 a roll is 10.67, so 11 rolls. Then the spare. Wallpaper is printed in batches and the colour drifts between them, so the roll you order in six weeks after a knock or a leak will not match the wall. One extra roll bought now, from the same dye lot as the rest, is cheap insurance and it is on by default here. Check the batch or dye lot number on every roll when the order arrives, before you cut a single strip.

7. 7. Read both waste numbers, then price it

   Cutting waste compares the paper you take off the rolls with the paper on the wall, and it is the figure the trade means by 10 to 15 percent on a straight match and 20 to 25 on a half drop. Total waste adds the remnant left unused on every roll, and on a single accent wall it can reach 40 percent because you still buy whole rolls. Both are honest and they answer different questions: cutting waste tells you whether your repeat and drop are sensible, total waste tells you what you actually paid for paper that never got hung. Then price it: rolls at your price, primer or sizing at about a gallon per 350 sq ft, adhesive at about a gallon per five double rolls for unpasted paper, and labor only if you want a yardstick to hold a quote against.

Worked scenarios, start to finish

Real jobs with the numbers carried all the way through, so you can see how the estimate is built and check your own figures against them.

The judgement calls a pro makes

Decisions the tool cannot make for you, and how someone who does this for a living thinks them through.

Whether to deduct doors and windows at all

This tool defaults to not deducting them, and that is deliberate. Paper is hung straight past an opening and cut out afterwards, which keeps a seam away from the corner of the opening where a tear or a lifted edge always starts, and it means the strip count above a door is the same as it would be on a blank wall. Deducting is right in one situation: a very wide opening where you genuinely intend to piece short lengths above and below, which saves paper and costs you a lot of fiddly matching. The large opening field handles the honest middle case automatically, deducting a cased opening or a wall of glass from the run only when it spans at least 80 percent of the wall height, because anything shorter still needs full length strips either side of it.

Wall by wall or one continuous run

Wall by wall is the default and it is the safe number, because every internal corner forces a fresh strip and the sliver left over is scrap. A continuous run wraps strips around the corners and usually saves a roll on a whole room. It is not free: it needs plumb walls, a corner that is genuinely square, and about half an inch of the strip turned onto the next wall and then over-lapped or double cut, which is a technique rather than a shortcut. Hang wall by wall if this is your first paper. Choose continuous if you have hung before and the room is true, and buy against the wall by wall number anyway if the difference is one roll, because the spare is the same roll either way.

Whether the extra roll is worth it

Keep it. Wallpaper is printed in batches and every batch drifts slightly in colour, which is what the batch or dye lot number on the label is for. Six weeks after the job, a chair back, a leak or a curious cat means one strip has to come off and go back on, and the roll you buy then will be from a different lot and will read as a patch under any side light. One roll bought now with the rest is the cheapest insurance on the job. Turn it off only when the paper is a plain random match texture where a slight shade difference will not show, or when the roll is genuinely expensive and you have measured twice.

Which roll format the seller will actually ship

In the United States paper is described and priced per single roll and then shipped as a double roll bolt, and this is where money gets lost. A listing at $45 a roll with a two roll minimum usually means $90 for one physical bolt of 33 ft, not two bolts. It matters for more than the price: a 16.5 ft single roll only makes one 8 ft 9 in drop, while the 33 ft double makes three, so the same wall costs 32 single rolls or 11 double rolls. If the listing does not say, ask for the roll length in feet before you order. That one number settles it, because the length is what the strip method actually uses.

Where to hang the first strip

Not in a corner, and not from a wall you assume is plumb. Snap or level a vertical line about one roll width in from the least visible corner, hang the first strip to that line, and work around the room in both directions so the inevitable pattern mismatch lands in that corner rather than over the sofa. On a feature wall with a strong motif, centre the pattern on the wall or on the focal point instead, and let the two end strips be the odd ones. The strip count does not change, but which strip gets the ugly cut absolutely does, and that is a decision you make with a pencil before you make it with a knife.

Trim allowance, and why 4 in is not padding

Two inches at the top and two at the bottom is the working default and it is not a fudge factor. Ceilings are rarely level, floors settle, and a strip cut exactly to a measured 96 in will run short at the far end of the wall where the ceiling has dropped half an inch. The allowance is what you trim off against a broad knife once the strip is on and plumb. Increase it to 6 in in an old house with visible settlement or where you measured a spread of more than an inch across the room, and only drop it to 2 in on a genuinely level new build where every measurement matched, because the saving is one repeat at most and the cost of getting it wrong is a whole strip.

Whether the paper needs sizing, and what adhesive to buy

Sizing or a wallpaper primer does two jobs: it gives the paste something consistent to grab, and it lets you strip the paper off later without pulling the drywall face with it. On new or freshly painted drywall it is worth the gallon. On sound, previously papered and stripped plaster it is close to essential. Adhesive depends on the paper: prepasted paper needs only water, unpasted needs a clay or wheat based paste applied to the paper and booked, and paste the wall non-woven needs paste rolled onto the wall itself, which is the easiest of the three by a distance. A gallon covers roughly five double rolls. If you are choosing a paper and have never hung one, choose a paste the wall non-woven and the whole job gets easier.

Common mistakes, and the fix

• × Dividing wall area by 56 sq ft a roll and adding 10 percent for waste.

  ✓ That is the area method and it under-buys on any tall drop and any real repeat, because it cannot see the offcut at the end of a roll. Divide the roll length by the cut length instead: a 33 ft roll cut into 8 ft 9 in drops gives 3 drops, and the 81 in left over buys you nothing. On a 12 by 12 room the area method says 8 rolls and the wall needs 11.

• × Ordering single rolls when the retailer ships double roll bolts.

  ✓ Read the roll length in feet, not the word on the price. Sixteen and a half feet is a single, 33 ft is a double, and US listings routinely price the single and ship the double. This tool states the answer in both units for exactly that reason: 11 double rolls is 22 single rolls, and a shop that quotes you 22 is quoting the same paper.

• × Ignoring the pattern repeat because the wall area has not changed.

  ✓ The repeat changes the cut length, and the cut length changes how many drops come off a roll, which is the only thing that decides the order. An 8 ft 4 in drop with no repeat gives 3 drops from a 33 ft roll with 16 in to spare. The same drop on a 25 in repeat cuts at 10 ft 5 in and gives 3 with almost nothing left, and one more inch of ceiling would drop it to 2.

• × Forgetting the trim allowance and cutting exactly to the wall.

  ✓ Add 2 in at the top and 2 in at the bottom before any repeat rounding. Ceilings are not level, and a strip cut to a measured 96 in will run short at the end of the wall where the ceiling has dropped. The allowance is trimmed off with a broad knife after the strip is hung and plumb, which is far easier than trying to hang a strip that is exactly right.

• × Measuring the ceiling height in one place.

  ✓ Measure it at three points across the room and use the tallest. An inch of variation is normal in any house that has settled, and on a patterned paper an extra inch can push every drop up a whole repeat, which on a 25 in repeat and 32 strips is 66 ft of paper, two whole rolls, decided by where you happened to hold the tape.

• × Sizing peel and stick panels on the printed panel width.

  ✓ Panels overlap about an inch so the pattern lines up, so a 24 in panel covers 23 in of wall. Across a 10 ft wall that hidden inch is 5 in of coverage you did not get, which is the difference between five panels and six. Use the coverage width, not the product width, and check whether the seller quotes coverage already.

• × Skipping the extra roll, then needing one after a repair.

  ✓ Buy the spare with the order and keep the label. Dye lots drift between print runs, so a roll bought later will read as a patch under side light no matter how carefully you match the pattern. Check that every roll in the delivery carries the same batch number before you start, because a mixed delivery has the same problem inside a single job.

• × Assuming a paper will hang on a tall stairwell wall because the square footage works out.

  ✓ Check the drop against the roll length first. A 14 ft stairwell wall needs a 172 in drop, and a 16.5 ft single roll is 198 in, so it makes exactly one drop and wastes 26 in every time. A 20 ft wall needs a drop longer than any standard roll, which means a made to measure mural or a custom bolt. This tool says so instead of returning a large number.

Material and unit specifics

The roll formats, and the coverage each one really gives

A US double roll is 20.5 in by 33 ft, about 56 sq ft, and it is the standard American bolt. A US double roll wide is 27 in by 27 ft, about 60 sq ft, and its extra width means fewer seams but its shorter length can cost you a drop. A US single roll is 20.5 in by 16.5 ft, about 28 sq ft, and it is half a bolt: mostly a pricing unit rather than something anybody ships. A euro roll is 52 cm by 10.05 m, which converts to 20.5 in by 33 ft, so it is a US double in metric clothing. Nominal coverage is a marketing number in every case, because none of it is usable unless it comes off the roll in whole drops.

Pattern repeat and the three match types

The repeat is the vertical distance before the design starts again, printed on the label in inches or centimetres. A random or free match, which is most grasscloths, textures and vertical stripes, has no alignment at all, so the cut length is just the drop plus trim and waste is lowest. A straight match lines the pattern up level across every seam, so each drop is cut at a whole number of repeats. A half drop, sometimes written as offset, drops alternate strips by half a repeat, which gives a diagonal rhythm across the wall and costs you half a repeat of roll length on every strip after the first on a roll. Repeats commonly run from about 10.5 in to 36 in, and the bigger the repeat the more the match type matters.

Non-woven, traditional, peel and stick and grasscloth

Non-woven is the modern default: a paper and synthetic fibre blend, dimensionally stable, hung paste the wall, and it strips off dry in whole sheets years later. Traditional paper is pulp or vinyl on a paper backing, hung paste the paper with a booking time while it expands, and it is less forgiving because it grows on the table and shrinks on the wall. Peel and stick is a self adhesive vinyl sold in panels, genuinely removable, and completely dependent on a smooth cured surface. Grasscloth is a natural fibre bonded to a paper backing, always a random match, and it has visible seams and colour variation by design, so it is hung with deliberate paneling rather than an attempt at invisibility.

Paste the wall against paste the paper

Paste the wall means rolling adhesive onto the wall and hanging the paper dry off the roll, which works only with non-woven papers that do not expand when wet. It is faster, cleaner, needs no pasting table and no booking time, and it is what to choose if you have never hung paper. Paste the paper means applying adhesive to the back of each strip on a table and folding it paste to paste for a booking time of typically five to ten minutes so it can expand before it goes up. Skip the booking and the strip expands on the wall instead, which shows as bubbles and open seams a day later. Prepasted paper is the third case: the paste is already on the back and is activated in a water tray, and it still needs its booking time.

Dye lots and batch numbers

Every roll label carries a batch, run or dye lot number, and it exists because ink colour drifts between print runs by a small amount that is invisible in the shop and obvious on a wall. Order the whole job at once so it comes from one lot, check that every roll in the delivery matches before you cut anything, and keep the spare roll with its label so a repair years later starts from the right batch. If a delivery does arrive mixed, use the odd rolls on the least visible wall or behind furniture rather than distributing them evenly, because a single boundary is far less visible than a gradient.

The substrate, and why it decides more than the paper does

Paper goes on smooth, sound, clean and sealed. New drywall should be finished to at least level 4 and primed with a wallpaper primer or sizing, because bare paper face will tear when the paper is stripped later. Peel and stick is stricter: it wants a level 4 finish or better, a satin or eggshell paint, and a full cure of about four weeks, and it will lift at every seam on flat paint, on texture, or on anything fresh. Old plaster wants cracks filled and a sizing coat. Existing wallpaper should come off rather than be papered over, because the new paste re-wets the old paste and both layers come away together.

2026 planning prices in the US

As a mid band range: a US double roll of everyday patterned paper is about $40 to $75, designer and hand printed papers run $150 to $400 a double roll, and peel and stick panel sets are about $40 to $70. Wallpaper primer or sizing is about $25 to $35 a gallon and covers roughly 350 sq ft. Clay or wheat paste is about $18 to $28 a gallon and covers roughly five double rolls. Professional installation is commonly quoted per roll, typically $35 to $65 for a straightforward room and more for a stairwell, a half drop or a heavy grasscloth, and removal of old paper is quoted separately. Every one of these is an editable default on this page, because a national average is nobody's real price.

Reading your result

The headline roll count is an order quantity in a specific unit, so read the unit before you read the number. Eleven double rolls and 22 single rolls are the same paper, and a shop that quotes either one is quoting the same job: the mistake to avoid is ordering 11 when the price was per single, or 22 when the shipping unit is a bolt. Under it, the strips per roll figure is the one that tells you whether the order is comfortable or tight. Three drops from a roll with 81 in left over is comfortable, because a mis-cut still leaves you options. Three drops with 4 in left over means one extra inch of ceiling somewhere in the room drops you to two drops a roll and blows the order apart, and that is when it is worth going back and re-measuring the height at every wall. The two waste numbers answer different questions. Cutting waste is about your paper and your wall: a straight match sitting in the 10 to 15 percent band is normal, a half drop at 20 to 25 percent is normal, and anything far above suggests a big repeat on a tall drop, which is worth knowing before you buy rather than after. Total waste includes the remnant left on every roll and is always higher, dramatically so on a single accent wall, where buying three whole rolls to cover 96 sq ft of wall is simply what buying whole rolls costs. Neither number is a fault to fix, they are the price of the format. In the ledger, treat everything as a shopping list you wrote yourself. The roll line is the only figure that is really fixed by the geometry; the primer, adhesive and labor lines are planning numbers to edit toward your own quotes. If the tool refuses to give you a roll count and says the drop is longer than the roll, believe it: that is not a rounding problem, it is a paper that physically cannot cover that wall in one piece, and the answer is a longer bolt or a made to measure mural rather than a smaller trim allowance.

Limitations

• This is a materials planning estimate, not a quote and not an order. Confirm the roll width, roll length, repeat and match type against the actual product page before you buy, because those four numbers drive everything here.
• Flat, vertical, rectangular walls. Sloped ceilings, dormers, stairwell walls with a raking cut, curved walls and arched recesses need to be measured by hand or broken into rectangles you enter as separate walls.
• Ceilings and stairwells are out of scope. Both are hung to different rules, both are two person jobs, and a stairwell drop often exceeds any standard roll length.
• Murals and made to measure panels are sized to your wall by the manufacturer from their own template, so use their measuring guide rather than this page. The panel mode here is for repeating peel and stick panel products sold in sets.
• The strip count assumes strips are hung vertically, which is the normal case. Horizontal or railroaded hanging, used on some grasscloths and wide vinyls, changes the arithmetic completely.
• Openings affect the run only under the rules stated: standard doors and windows do not shorten it unless you turn deduction on, and a large opening only does so once it spans 80 percent of the wall height.
• Prices are editable mid band US planning figures for 2026, not quotes. Paper prices in particular span an order of magnitude between an everyday pattern and a hand printed design.
• Imperial units in feet and inches, consistent with the rest of the site. A euro roll is offered as a preset in its US equivalent dimensions rather than in centimetres and metres.

Frequently asked questions

How many rolls of wallpaper do I need for a 12x12 room?

For a 12 by 12 room with an 8 ft ceiling, on standard 20.5 in by 33 ft double rolls with a 21 in straight match repeat, you need 11 double rolls, which is 22 single rolls, plus one spare from the same dye lot. The arithmetic: the perimeter is 2 x (12 + 12) = 48 ft, each of the four walls takes ceil(144 / 20.5) = 8 strips so 32 strips in total, the drop is 96 in plus 4 in of trim rounded up to 5 repeats of 21 in = 105 in, and a 33 ft roll gives floor(396 / 105) = 3 drops. 32 strips at 3 a roll is 11 rolls. Hanging in one continuous run around the room instead of wall by wall drops it to 10. Note how far that is from the area method: 384 sq ft divided by 56 sq ft a roll plus 10 percent is 8 rolls, which would leave you three rolls short. With no repeat at all, on a random match paper, it is still 11 rolls, because the roll still only yields 3 drops of 100 in.

How much wallpaper do I need for a 10x10 or an 8x12 wall?

A 10 ft wide by 10 ft tall wall takes 6 strips: 120 / 20.5 = 5.85 rounded up. The drop is 120 in plus 4 in of trim, rounded up on a 21 in repeat to 126 in, and a 33 ft roll gives floor(396 / 126) = 3 drops, so 2 double rolls cover it, 3 with a spare. An 8 ft tall by 12 ft wide wall takes 8 strips at a 105 in cut length, 3 drops a roll again, so 3 double rolls and 4 with a spare. Those two walls are almost the same square footage, 100 against 96, and they need a different number of rolls, which is the clearest possible demonstration that square footage is not what decides a wallpaper order. Swap in your own repeat and roll length above and the numbers move again.

What is the difference between a single roll and a double roll of wallpaper?

A double roll is one continuous bolt of twice the length, and in the United States it is almost always what actually ships. A standard US single roll is 20.5 in by 16.5 ft, about 28 sq ft, and the double is the same width by 33 ft, about 56 sq ft. The trap is that retailers price and describe paper per single roll while selling and shipping it as a double roll bolt, so a listing at $45 a roll with a two roll minimum usually means one physical bolt for $90. It is not only a pricing question. The longer bolt gives you more usable drops: at an 8 ft 9 in cut length a 33 ft double roll yields 3 drops while a 16.5 ft single yields only 1, wasting 7 ft 9 in every time. That is why this page states the answer in both units and asks for the roll length in feet rather than the marketing name.

Do I subtract doors and windows when measuring for wallpaper?

Usually no, and this page defaults to not deducting them. Paper is hung straight past an opening and cut out afterwards, which keeps a seam away from the corner of the opening where lifting and tearing start, so the strip above a door costs the same as a strip on a blank wall. Deducting only makes sense on a genuinely large opening where you intend to piece short lengths above and below, and even then you trade paper for a lot of awkward pattern matching. This tool handles the honest middle case for you: a cased opening, a wall of glass or a fireplace breast entered in the large opening field comes off the run automatically once it spans at least 80 percent of the wall height, because anything shorter still needs full length strips beside it. The opening area is always subtracted from the net square footage used for sizing primer, whichever way you set the toggle.

What is a half drop match and why does it use more wallpaper?

A half drop, also written as offset match, means alternate strips start half a pattern repeat further down the roll, so the design runs diagonally across the wall instead of lining up level. It costs more paper for a specific mechanical reason: every strip after the first one cut from a roll has to advance half a repeat before the pattern is in the right place, so the roll capacity becomes floor((roll length + repeat/2) / (cut length + repeat/2)) instead of floor(roll length / cut length). A worked example: a 10 ft 5 in drop on a 25 in repeat and a 33 ft roll gives floor(396 / 125) = 3 drops on a straight match, and floor(408.5 / 137.5) = 2 on a half drop. On a 12 by 12 room with 9 ft ceilings that is 16 rolls instead of 11, roughly $275 of extra paper on identically priced rolls. The penalty is not always that steep, so run both before you choose a colourway.

How do I calculate peel and stick wallpaper?

Count panels, not square feet, and use the coverage width rather than the printed width. Panels overlap about 1 in so the pattern lines up, so a 24 in panel covers 23 in of wall. Panels are ceil(wall width / coverage width), so a 10 ft wall is ceil(120 / 23) = 6 panels, and sets are ceil(panels / panels per set), which at two to a set is 3 sets. Then check the height: the panel must be taller than the wall, because a horizontal join across a peel and stick wall is very hard to hide, and 9 ft panels on an 8 ft wall leave a comfortable 12 in to trim. The surface matters more than the arithmetic. Peel and stick needs a smooth, fully cured, satin or eggshell painted wall, which means a level 4 drywall finish or better and about four weeks after painting. On flat paint, on texture or on fresh paint it lifts at the seams no matter how many panels you buy.

How many yards of wallpaper do I need for a 12x12 room?

About 121 linear yards for a 12 by 12 room with an 8 ft ceiling on a 21 in straight match repeat. That comes from the roll count rather than from the area: 11 double rolls of 33 ft each is 363 ft, which is 121 yards. If the paper is sold by the yard rather than by the roll, size it from the strips instead, because you still buy whole drops: 32 strips at an 8 ft 9 in cut length is 280 ft, or about 94 yards of paper actually on the wall, and the difference between 94 and 121 is the remnant you cannot use at the end of each roll. Buying 94 yards as continuous yardage is fine; buying 94 yards in 33 ft rolls is not, and that gap is exactly what the strip method exists to expose. In square feet, the same room buys 620 sq ft to cover 384 sq ft of wall.

Should I remove old wallpaper first, or can I paper over it?

Remove it. New paste re-wets old paste, so the two layers come away together and you find out at the worst moment, usually after the third strip. Papering over is only defensible over a single sound layer of well stuck lining paper, and even then the old seams telegraph through. Removal is a different job from installation and is priced separately, typically as a per square foot or per room charge, and it goes much faster with a steamer and a scoring tool than with a spray bottle. Once the old paper is off, wash the residual paste completely, fill and sand any damage, and prime with a wallpaper primer or sizing before the new paper goes up. If the drywall face tore during removal, skim and finish it properly first, because paper does not bridge a torn paper face, it highlights it. This calculator sizes new work, not removal.