🎨 Wallpaper Calculator

How to Calculate Wallpaper

Wallpaper is sold by the roll, but what a roll yields depends on your wall height, because paper is hung in whole strips and the remainder is offcut. A 21 in × 33 ft roll is 57.8 sq ft on paper; on an 8 ft wall it gives three strips, about 42 sq ft usable. On a 9 ft wall it still gives three strips; on an 11 ft wall only two.

Basic Formula

Step by Step

• Calculate wall area: Room perimeter × wall height
• Subtract openings: Doors (~21 sq ft each), Windows (~15 sq ft each)
• Calculate roll coverage: Roll width × Roll length
• Work in whole strips: a roll yields a whole number of drops and the remainder is offcut — divide roll length by cut length and round down
• Pattern repeat: If patterned, add extra for matching

How to Measure a Room for Wallpaper

Measuring for wallpaper is not the same job as measuring for paint. Paint is bought by area and does not care what shape that area is. Wallpaper arrives as a fixed-width strip that has to run from ceiling to baseboard in one piece, so two numbers matter more than the area does: the perimeter, which decides how many strips you need, and the wall height, which decides how long each one has to be.

1. Measure the perimeter. Run the tape along the base of every wall you intend to paper and add the lengths together. For a rectangular room that is 2 × (length + width) — a 12 ft × 14 ft room has a 52 ft perimeter. Include the wall the door is on; you deal with the door in a later step, not by skipping the wall.
2. Measure the height at both ends of every wall. Floors settle and ceilings are rarely level, and in an older house an inch of variation across a single wall is normal. Use the largest height you find — every strip is cut to the same length, so the shortest cut is the one that comes up short at the baseboard.
3. Add a trim allowance. Add at least 4 inches to that height, 2 in at the top and 2 in at the bottom, so there is something to trim off against the ceiling line and the baseboard. On a visibly out-of-level ceiling, use 4 in at each end.
4. Record openings individually. Write down the width and height of each door, window and cased opening rather than just counting them, because size is what decides whether an opening actually saves you any paper.
5. Note the obstacles. Chimney breasts, built-ins, radiators, stair strings and dormer cheeks all add strips that a perimeter measurement cannot see.

What to Deduct — and What Not To

The calculator above deducts a standard door at 21 sq ft (roughly 3 ft × 7 ft) and a standard window at 15 sq ft. Those are fair averages, but the honest rule is narrower: only deduct an opening big enough to swallow a whole strip's worth of length.

• Deduct doors. The piece above a door is 12 to 18 inches long and nobody buys paper for it — it comes out of an offcut. A door genuinely removes most of a strip.
• Deduct large openings. Patio sliders, picture windows and wide cased openings — anything over roughly 4 ft wide or 5 ft tall — remove real paper.
• Do not deduct a standard window. You still hang a full-length strip straight past it and cut the hole out afterwards. The two offcuts, above and below, are usually at the wrong point in the pattern to use anywhere else.
• Do not deduct anything if your repeat is over about 12 inches. At that repeat size the offcuts almost never land where you need them. Set the window count to zero and let the extra be your margin.
• Never deduct for furniture. Paper behind the wardrobe and behind the bed. Furniture moves; a bare patch does not.

Measuring a Single Feature Wall

For one wall, skip the perimeter entirely. Measure that wall's width, divide by the strip width to get the strip count, and multiply by the cut length. A 12 ft wall in 20.5 in paper is 144 ÷ 20.5 = 7.02, which means 8 strips: seven full ones and a narrow fill in the corner. Center the first strip on the wall rather than starting in a corner, so the pattern stays symmetrical and both cut edges land where nobody looks. Our accent wall calculator works wall-first instead of room-first.

The Wall Has to Be Right First

Wallpaper hides far less than people expect. It telegraphs bumps, ridges and roller stipple, and a seam that lands over a proud drywall joint will lift. Anything you can feel with a flat hand you will see through the paper. A wall about to be papered wants the same flatness as one about to take a gloss paint — a Level 4 finish at minimum, and a Level 5 skim under a thin or light-colored paper. Fill, sand, dust off, then prime with a wallpaper primer or sizing before a single strip goes up.

Standard Roll Sizes

• American Single Roll: 21" wide × 33' long (~57.8 sq ft gross; 3 strips ≈ 42 sq ft usable on an 8 ft wall)
• American Double Roll: 21" wide × 66' long (~115.5 sq ft gross; 7 strips ≈ 98 sq ft usable on an 8 ft wall)
• European Roll: 20.5" wide × 33' long (~56 sq ft)

Tip: Many wallpapers are sold as double rolls. Check the packaging carefully.

Types of Wallpaper

Choosing the right wallpaper type affects both the look and the installation process.

Standard Pre-Pasted

The most common type. Adhesive is pre-applied to the backing — just activate with water. Works well for most rooms and is widely available in thousands of patterns.

Peel & Stick

Self-adhesive wallpaper that sticks directly to the wall. Easy to apply, reposition, and remove without damaging surfaces. Ideal for renters and accent walls. Slightly thinner than traditional wallpaper.

Grasscloth & Natural Fiber

Made from woven natural materials like jute, seagrass, or bamboo. Creates a rich, textured look. More expensive ($60–200+ per roll) and requires professional installation for best results.

Vinyl

The most durable and moisture-resistant option. Easy to clean with a damp cloth. Best for kitchens, bathrooms, and high-traffic areas. Available in realistic textures that mimic grasscloth, brick, and wood.

How Much Does Wallpaper Cost?

Wallpaper costs vary widely based on type, brand, and pattern complexity.

• Budget-friendly: $20–40 per roll — basic patterns, peel & stick options
• Mid-range: $40–80 per roll — quality pre-pasted, popular designs
• Premium: $80–150+ per roll — designer patterns, grasscloth, metallic finishes
• Luxury: $150–300+ per roll — hand-printed, artisan, or custom wallpaper

Take a standard 12×12 ft room with 8 ft ceilings. The perimeter is 48 ft, so the walls are 384 sq ft; deduct a door and a window and about 350 sq ft needs covering. At the ~42 sq ft a single roll actually yields on an 8 ft wall (three strips, once trim is lost), that is 9 single rolls — or 5 double rolls, which is how most patterns ship.

At the prices above that puts the paper alone at roughly $180–360 budget, $360–720 mid-range, and $720–1,350 premium. Professional installation adds $200–500 per room. Count rolls before you price them: the roll count, not the price per roll, is what usually surprises people.

Wallpaper vs. Paint: Which Is Right?

Choose Wallpaper When:

• You want patterns, textures, or visual depth that paint can't achieve
• You're creating a statement or accent wall
• You want a look that lasts 10–15 years without touch-ups
• You're covering imperfections in older walls

Choose Paint When:

• Budget is tight ($30–60 for a full room vs. $120–600+ for wallpaper)
• You change colors frequently or like to update often
• The room has lots of corners, outlets, or irregular surfaces
• You're doing a quick refresh in a day

Many designers combine both: painted walls with one wallpapered accent wall. Use our Paint Calculator to estimate paint for the other walls.

Pattern Repeat and Waste

Pattern repeat is the vertical distance before the design starts over, and it's the reason wallpaper estimates aren't simple area division. Every strip must begin at the same point in the pattern, so you cut off and discard part of each drop to line it up.

A straight match lines up at the same height on every strip. A half-drop match steps down by half the repeat on alternate strips, which looks more natural but wastes noticeably more. Check which one you're buying — the label will say.

Order every roll in one batch and check the run number. Wallpaper is printed in batches and color varies measurably between them. A roll bought later to finish a wall will usually be visibly different, and unlike paint there's no fixing it.

Preparation

1. Prime with wallpaper primer or sizing. On bare drywall this is what makes the paper strippable later — without it, removal takes the drywall face with it.
2. Fill and sand. Wallpaper telegraphs every bump; it hides far less than people expect.
3. Plumb your first line. Never trust a corner or a ceiling to be straight. Snap a vertical line and hang the first strip to it.
4. Start away from the focal point and work outward in both directions, so the inevitable pattern mismatch lands in the least visible corner.
5. Book pre-pasted paper — fold the pasted sides together and let it rest the stated few minutes. This lets the paper expand before it's on the wall, which prevents bubbles and seam gaps.
6. Smooth from the center out with a smoothing brush, and wipe adhesive off the surface as you go rather than after it dries.

How to Read a Wallpaper Label

Every bolt carries a label or a printed band with a block of symbols and three numbers, and between them they tell you everything the calculator needs. Photograph it before the wrapper goes in the bin.

The Three Numbers

• Roll dimensions. Metric papers give them in meters — 0.53 m × 10.05 m is the near-universal European roll, which is 20.5 in × 33 ft. American papers give inches and feet. Enter the physical width and length of the bolt in your hand, not the "single roll" figure printed in the catalogue.
• Pattern repeat and offset. Usually written as a pair such as "64/32", meaning the design repeats every 64 cm (25 in) and each strip steps down by 32 cm (12.5 in). A repeat printed as "64/0" is a straight match. No figure at all means free match.
• Batch, run or lot number. The number that decides whether two rolls are the same color. Check it on every roll in the box before you start cutting, not after.

The Symbols

Symbol sets are broadly standard across European and American manufacturers, but the exact icons vary by brand, so read the key printed on the label rather than relying on memory.

Straight match versus half-drop, in practice. On a straight match the same point of the design sits at the same height on every strip, so every cut can start at the same place in the roll. On a half-drop, strip two starts half a repeat below strip one, strip three matches strip one again, and so on. Cut them all sequentially from a single roll and you throw away roughly an extra half repeat on every second strip. The fix is to cut odd strips from one roll and even strips from another, alternating between two rolls of the same batch. It is the single most useful trick on a large half-drop paper.

Roll Coverage, Double Rolls and Yardage

Roll coverage is where most wallpaper orders go wrong, because three different numbers all get called "coverage": the nominal area of the bolt, the area a retailer quotes per "single roll", and the area that actually ends up stuck to a wall. They can differ by a factor of two.

Single Rolls, Double Rolls and What Actually Ships

In North America wallpaper is priced per single roll but almost always sold as a double roll — one continuous bolt. The single roll is a pricing convention left over from when paper really did come in short lengths, and in most lines you cannot buy one. When a listing says "$45 per single roll, sold in double rolls", the thing arriving in the box is one bolt, it costs $90, and it is the unit your strip count has to work from.

• Metric bolt (most common worldwide): 0.53 m × 10.05 m = 20.5 in × 33 ft, about 56 sq ft. One roll in Europe and the UK; a double roll in the US.
• American 21 in bolt: 21 in × 33 ft, about 57.75 sq ft. This is the calculator's default.
• American wide bolt: 27 in × 27 ft, about 60 sq ft. Fewer, wider strips, but a shorter roll — which cuts both ways, as the table below shows.
• Contract and commercial goods: 54 in wide, sold by the linear yard rather than by the roll.

Widths and lengths vary by manufacturer and by region, and the 2% difference between 20.5 in and 21 in is enough to change a strip count at the margin. Measure the bolt or read the label rather than assuming.

Why 56 sq ft Only Covers About 40

A bolt is a fixed length and you can only take whole strips out of it. Divide the roll length by the cut length, round down, and multiply back by the finished wall height, and the honest coverage falls out. For a 20.5 in × 33 ft bolt with a 4 in trim allowance and no pattern repeat:

That is before a single inch is lost to pattern matching or to corner cuts. Add a large repeat on top and a nominally 56 sq ft bolt lands nearer 40 sq ft of wall — exactly the figure in the waste table above. Note how uneven the sawtooth is: 8 ft and 11 ft ceilings are the expensive ones, because they fall just short of a whole extra strip.

Wallpaper Yardage

"Yardage" in wallcovering means linear yards, not square yards, and confusing the two is a genuinely expensive ordering error — one linear yard of standard 54 in contract goods is 1.5 square yards.

• Residential rolls in yards: a 33 ft bolt is 11 linear yards. If a supplier quotes 33 yards of a 20.5 in paper, that is three rolls.
• Contract and commercial vinyl is sold by the linear yard in 54 in width, usually in bolts of 30 linear yards — 405 sq ft nominal. Some mills offer 15 yd bolts or cut yardage at a premium.
• Worked conversion: 447 sq ft of coverable wall ÷ 13.5 = 33 linear yards. Add 20% for a 13–18 in repeat and you need 40 linear yards, which in practice means a 30 yd bolt plus a 15 yd bolt from the same run.
• Check strips, not just yards. A 9 ft 4 in cut is 3.11 linear yards, so a 30 yd bolt yields 9 whole strips, not 9.6. Nine strips of 54 in goods cover 9 × 9 × 4.5 = 364 sq ft against 405 nominal.

Strips Per Roll: The Number That Decides Your Order

Area gets you a sanity check. Strips get you an order. Every wallpaper job comes down to how many full-length pieces you can cut from a fixed-length bolt, and the answer is always a whole number.

Round Down, Always

A roll that works out at 3.9 strips gives you three. There is no such thing as a partial strip — wallpaper cannot be joined end to end without the join being obvious — so the last 8 ft of a 33 ft roll is only good for fills over doors and under windows. This is why the arithmetic is so unforgiving at the margins, and why five inches of cut length can cost a whole roll.

Getting the Cut Length Right

• Trim allowance: 4 in total is the minimum, 2 in at each end. Use 8 in in an old house with a wandering ceiling line.
• Random match: cut length is simply height + trim. Nothing else to add.
• Straight match, for ordering: height + trim + one full repeat. This is the safe rule, and it is what the calculator above assumes.
• Straight match, when you are actually cutting: round (height + trim) up to the next whole multiple of the repeat. A 9 ft wall with 4 in trim is 112 in; with a 10.5 in repeat the next whole multiple is 11 × 10.5 = 115.5 in, not the 122.5 in the safe rule gives. You still lose up to one repeat finding the right start at the head of each roll, which is exactly what the safe rule is paying for.
• Half-drop: order on the safe rule, and cut alternate strips from two different rolls of the same batch so you are not discarding half a repeat on every second drop.

Counting the Strips You Need

Divide the perimeter by the strip width and round up. A 52 ft perimeter in 20.5 in paper is 624 ÷ 20.5 = 30.4, so 31 strips. That figure assumes you cut a strip at each inside corner and start the next wall with the remainder, which is standard practice — you have to re-plumb at every corner anyway, because no corner is truly vertical.

If you cannot reuse those corner offcuts — a large repeat, an expensive paper, or a room where you want a full-width strip leading each wall — count wall by wall instead and round up on every wall. The same room comes out at 9 + 9 + 8 + 8 = 34 strips. The gap between 31 and 34 is a whole roll, and it is the biggest single source of disagreement between two people estimating the same room.

Why a Percentage Waste Factor Reads Low

The common rule of thumb — take the roll’s nominal area and knock 15% off for waste — is a reasonable average, but it hides the thing that actually decides your order: paper is hung in whole strips, so a roll yields a whole number of them and the remainder is offcut. The calculator above works in strips for that reason. The gap is worst at an 8 ft ceiling, where a 33 ft roll reaches 3.96 strips and delivers three: a 40 ft run of 8 ft wall needs 24 strips, which is 8 rolls, or 448 sq ft of paper for 320 sq ft of wall. A flat 15% would have told you 6 rolls.

Worked Example: A 12 × 14 ft Bedroom

A 12 ft × 14 ft bedroom with 9 ft ceilings, one standard door and one 3 ft × 4 ft window. The paper is a metric bolt, 20.5 in × 33 ft, straight match, with a 10.5 in repeat.

Step 1 — Area

Perimeter is 2 × (12 + 14) = 52 ft. Gross wall area is 52 × 9 = 468 sq ft. Deduct the door at 21 sq ft. Leave the window in — it is small and the repeat is over 10 in, so those offcuts will not get reused. Coverable area is 447 sq ft.

Step 2 — Cut length

9 ft is 108 in. Add 4 in of trim and one full 10.5 in repeat: 122.5 in, or 10 ft 2.5 in per strip.

Step 3 — Strips per roll

The bolt is 33 ft, or 396 in. 396 ÷ 122.5 = 3.23, so 3 strips per roll. Cutting to the tight rule instead (115.5 in, a whole multiple of the repeat) gives 3.34 even after losing a repeat at the head of the roll — still three. Nothing about this paper gets a fourth strip out of a 33 ft bolt at this ceiling height, which is a useful thing to know before you start hoping.

Step 4 — Strips needed

The perimeter is 624 in and the strip is 20.5 in wide, so 624 ÷ 20.5 = 30.4 → 31 strips. The door removes about one strip's worth, since the short pieces over and beside it come out of offcuts: 30 strips.

Step 5 — Rolls

30 strips ÷ 3 per roll = 10 rolls. Run the same figures through the calculator at the top of this page — perimeter 52, height 9, 1 door, 0 windows, roll 20.5 in × 33 ft, repeat 10.5 in — and it also returns 10. Two independent methods agreeing is the result you want before you spend money.

Step 6 — The conservative check

Now count wall by wall. The 14 ft walls take 9 strips each (168 ÷ 20.5 = 8.2) and the 12 ft walls take 8 each (144 ÷ 20.5 = 7.02, with the eighth a half-inch sliver). That is 34, less one for the door, so 33 strips — 11 rolls. With a repeat this size, assume you will not be able to place every corner offcut, and order the 11.

Step 7 — The order

Eleven rolls, all from one batch, ordered in one go. That is 616 sq ft of paper for 447 sq ft of wall, a 38% overage, which sounds wasteful until you break it down: roughly 18% goes to the three-strips-per-bolt cut, about 10% to corner rounding, and the rest to the pattern repeat. Keep the usable offcuts rolled up in a closet — a scald mark or a torn corner five years from now is a 20-minute repair with matching paper and a full re-paper without it. At $45–70 a bolt for a mid-range patterned paper that is roughly $500–770 in wallcovering, plus $30–50 for primer and paste.

Change one variable

Raise the ceiling to 10 ft and the safe cut length becomes 134.5 in, which is 2.94 strips per bolt — three strips become two and the order jumps from 10 rolls to 15. Cut to the tight rule instead (126 in, a whole multiple of the 10.5 in repeat) and you still get three, at 10 rolls. One foot of ceiling and one line of arithmetic is a $250 swing on this paper. Ceiling height and pattern repeat, not floor area, are what move the number — which is the whole argument for checking strips before you check square footage.

Awkward Walls: Stairwells, Sloped Ceilings and Dormers

Everything above assumes a rectangular room with walls of one height. The moment that stops being true, area estimates stop working and you have to count individual drops.

Stairwells

The longest drop governs everything. On a typical two-story stairwell the strip running from the upper ceiling down to the tread below it is 13 to 18 ft — longer than half a bolt. Measure that drop first, then work across the wall in strip widths, measuring the drop at each position and adding 4 in of trim to each. Total the drops and divide by the roll length to get rolls for that wall. Do not use area here: on a stairwell the triangular offcut below each strip is waste unless the paper is a free match, and area estimating silently assumes it is not.

The bigger issue is access. Do not stand a ladder on stair treads. Hire a stair platform, or use an adjustable-leg ladder with a scaffold plank spanning to a step-up on the landing. A 16 ft pasted strip is heavy, floppy and needs both hands, and this is the wall in the house where a fall has the furthest to go.

Sloped Ceilings and Knee Walls

Treat every strip as its own length. Measure the drop at the left and right edge of each strip position and cut to the longer of the two, plus trim. On a patterned paper expect 30% waste or more on a sloped wall regardless of what the repeat table says, because the offcut triangles are the wrong shape for anything else.

Where a knee wall meets the slope you can either seam at the break or run one piece up and over it. Running over is far neater, but every strip is then the full combined length, so price both before deciding.

Dormers

Count the cheeks. A dormer has a face and two side cheeks, and each cheek needs at least one strip of its own no matter how narrow it is. Two dormers quietly add four strips to a room that measured as though it had none.

Chimney Breasts and Alcoves

Center the pattern on the face of the chimney breast and work outward in both directions. It is the focal point of the room and an off-center motif on it is the first thing anyone notices. That decision pushes the leftover widths into the returns and the alcoves, so count that wall strip by strip rather than by its overall length.

Curves, Bulkheads and Boxed-In Pipes

Anything you have to wrap costs a strip. Boxed-in soil pipes, bulkheads over cabinets and curved bay returns each need their own piece, and on a curve the paper has to be relief-cut and the seam will show. Add one strip per feature and move on. For genuinely irregular walls, break the shape into rectangles and triangles with the square footage calculator first, then convert the area to strips.

Estimating it and hanging it are two different skills. Our step-by-step guide to hanging wallpaper covers priming and sizing, plumbing the first line, booking, butt seams, corners, outlets and removal.

Frequently Asked Questions

What is pattern repeat?

Pattern repeat is the distance between where the pattern starts again. Larger repeats mean more waste when matching patterns between strips.

How much extra should I buy?

Always buy at least 1 extra roll (2 for large patterns). Dye lots vary, so running out mid-project can mean a visible mismatch.

Do I wallpaper behind furniture?

Yes, if possible. You may move furniture later, and partial wallpaper looks unfinished.

Can you wallpaper over existing wallpaper?

It's not recommended. Old wallpaper can bubble, peel, or create an uneven surface under the new layer. Best practice is to remove existing wallpaper, repair the wall, and prime before applying new wallpaper.

How long does wallpaper last?

Quality wallpaper lasts 10–15 years or more with proper installation. Vinyl wallpaper is the most durable, while grasscloth may show wear in high-traffic areas sooner. Peel & stick is designed for shorter-term use (3–5 years).

How do I calculate wallpaper rolls?

Multiply the wall perimeter by the height to get area, subtract large openings, then divide by the usable coverage per roll — which is less than the roll's stated area once pattern repeat is accounted for. A double roll nominally covers 56 sq ft but yields closer to 40 with a large repeat.

How does pattern repeat change how much I need?

Every strip has to start at the same point in the pattern, so you waste part of each drop. With a 0–6 inch repeat add about 10%; 7–12 inch, add 15%; 13–18 inch, add 20%; over 19 inches, add 25–30%. A half-drop match wastes more than a straight match at the same repeat size.

How many strips can I get from one roll?

Divide the roll length by your cut length (wall height plus the repeat plus about 4 inches of trim allowance). A double roll of 33 ft with a 9 ft cut length gives 3 full strips — the remaining 6 ft is usually only good for over-door or over-window fills.

Do I need to prime walls before wallpapering?

Yes, for anything but a previously papered wall in good condition. A dedicated wallpaper primer or sizing seals porous drywall so the adhesive doesn't soak in, and — critically — it lets you strip the paper later without destroying the drywall face. Papering directly onto bare drywall is close to permanent.

Where should I start hanging wallpaper?

Plumb a line near a corner and start there, working away from the room's focal point in both directions. The final seam will land in the least conspicuous corner where a pattern mismatch matters least — there's always a mismatch, since rooms are never exactly a whole number of strips around.

What's the difference between single and double rolls?

A single roll is 21" × 33' (~57 sq ft). A double roll is 21" × 66' (~115 sq ft). Most wallpaper in stores is actually priced and sold as double rolls, even though the coverage is listed per single roll. Always check the packaging to confirm what you're getting.

How do I measure a room for wallpaper?

Measure the perimeter at floor level, then measure the wall height at both ends of every wall and use the largest figure you find. Multiply perimeter by height for the gross wall area, deduct doors and any opening wider than about 4 ft, and add at least 4 inches to the height as a trim allowance before you work out cut lengths. Record each opening's size individually rather than just counting them — size is what decides whether it saves you any paper.

How do I calculate wallpaper square footage?

Multiply the room perimeter by the wall height. A 12 ft × 14 ft room has a 52 ft perimeter, so at 9 ft ceilings that is 468 sq ft gross; deduct 21 sq ft per door and leave standard windows in, giving 447 sq ft coverable. Square footage is only a sanity check, though — the number you actually order to is the strip count, because a roll yields whole strips and nothing else.

Do I subtract windows and doors when measuring for wallpaper?

Deduct doors and any opening big enough to swallow a whole strip's worth of length — patio sliders, picture windows, wide cased openings, anything over roughly 4 ft wide or 5 ft tall. Do not deduct a standard window: you still hang a full-length strip past it and cut the hole out, and the offcuts above and below are usually at the wrong point in the pattern to use elsewhere. If your repeat is over about 12 inches, leave every window in.

How many yards of wallpaper do I need?

Wallpaper yardage means linear yards, not square yards. Standard 54-inch contract goods give 13.5 sq ft per linear yard, so divide your coverable square footage by 13.5 and add the waste percentage for your repeat. 447 sq ft with a 13–18 in repeat works out at 40 linear yards, which is a 30 yd bolt plus a 15 yd bolt. For residential rolls, a 33 ft bolt is 11 linear yards.

What is the difference between a straight match and a half-drop match?

On a straight match the design sits at the same height on every strip, so every cut can start at the same point in the roll. On a half-drop (offset) match, alternate strips step down by half the repeat — it looks more natural but wastes more paper at the same repeat size. The fix is to cut odd strips from one roll and even strips from a second roll of the same batch, which recovers most of the extra waste.

How much wallpaper do I need for a 12 × 14 ft room?

With 9 ft ceilings, one door and standard 20.5 in × 33 ft rolls, the perimeter is 52 ft and the coverable area is 447 sq ft. The bolt yields 3 strips at that ceiling height and the room needs about 30 strips, so 10 rolls — 11 if a large pattern repeat stops you reusing corner offcuts. Order 11, all from one batch.

Why does a 56 sq ft roll only cover about 40 sq ft?

Because a bolt only yields whole strips. A 33 ft roll cut into 8 ft 4 in lengths gives three strips, not 3.96, and three strips of 20.5 in paper cover 41 sq ft of an 8 ft wall. Add pattern matching and corner cuts on top and a nominally 56 sq ft double roll lands nearer 40 sq ft. Ceilings of 8 ft and 11 ft are the worst offenders, because they fall just short of a whole extra strip.

How much extra length should I add for trimming?

At least 4 inches on top of the wall height — 2 in at the ceiling and 2 in at the baseboard. Use 4 in at each end where the ceiling line is visibly out of level, which is normal in older houses. That allowance is part of the cut length, so it feeds straight into how many strips you get from a roll.

How do I measure a stairwell for wallpaper?

Measure the longest drop first, usually from the upper ceiling to the tread directly below it, commonly 13 to 18 ft. Then work across the wall in strip widths, measure the drop at each position, add 4 in of trim to each, total the lengths and divide by the roll length. Do not estimate a stairwell by area — the triangular offcuts are waste unless the paper is a free match.

Can I use a paint calculator to estimate wallpaper?

No. Paint is bought by area and covers any shape; wallpaper comes in fixed-width strips that have to run full height in one piece, so ceiling height, roll length and pattern repeat change the answer in ways area cannot capture. Use the paint calculator for the ceiling and trim — and the paint sheen guide to pick a finish for them — and this calculator for the paper.