Every formula behind every calculator on this site, the product dimensions each one assumes, where those dimensions come from, and what these tools deliberately will not do. If a number we give you looks wrong, this page is how you check our working.
All six calculators convert your inputs to feet internally, whichever units you type in, then do the arithmetic once. Three principles apply throughout.
We always round up, never down. A partial roll is a roll you have to buy. Every division that produces a fraction of a roll, panel or box is rounded up to the next whole unit.
Buffers are applied to strips, not to the final unit count. This matters more than it sounds. Adding 15% to a count of 4 rolls gives you 4.6, which rounds to 5, a 25% real increase. Adding 15% to the 26 strips those rolls are cut from gives you 30 strips, which is a true 15%. Applying the buffer at the strip level is the difference between an estimate and a guess dressed up as one.
We never assume your wall is a rectangle you can cover edge to edge. Wallcovering is hung in vertical strips of fixed width. A 44 foot perimeter divided by a 20.5 inch roll is 25.76 strips, and you cannot buy 0.76 of a strip. That rounding up is real material, and it is why area-based estimates that simply divide square footage by roll coverage come in low.
The wallpaper calculator uses the drop method, which is how the trade estimates papered walls. It works in strips rather than in area, because that is how paper is cut and hung.
Step one, the cut length. Your wall height plus a trimming allowance of 12 inches, 6 at the ceiling and 6 at the skirting. Published trade guidance runs from about 5 cm to 15 cm at each end; we use 6 inches because that is what Rochelle cuts, and it lands on 15 cm, the top of that range. Cutting short is the expensive mistake: a generous trim costs an inch of paper, a short one costs a whole strip.
Then, if the paper has a pattern, that length is rounded up to a whole number of pattern repeats. This is the part most calculators get wrong. They add one repeat to every drop, which is always enough and usually too much. The real rule is that consecutive strips can only meet if each cut contains a whole number of repeats, so the cut is ceil((height + trim) / repeat) × repeat. On an 8 ft wall with a 10.5 in repeat that is 9.63 ft, not the 9.88 ft you get by adding a full repeat. Over a room, that difference is a roll.
A half-drop (offset) match starts each alternate strip half a repeat down, so it needs an extra half repeat of allowance before the rounding. A random or free match, which covers most plains, textures and many stripes, needs no repeat allowance at all, so we ignore the repeat field entirely when you select it rather than quietly charging you for waste that does not exist.
Step two, drops per roll. Roll length divided by cut length, rounded down. A 33 ft roll that yields 3.4 cuts yields 3. The remainder is offcut.
This is a step function, not a slope, and it is the single most useful thing on this page. A 33 ft roll gives three drops as long as your cut stays under 11 ft. On an 8 ft ceiling that means a repeat of up to 24 inches costs you nothing extra at all. Go one inch past it and every roll drops to two cuts, and your order jumps by half. If the calculator tells you the cut divides almost exactly into the roll, it says so, because at that point a bolt that runs slightly short or a ceiling that is out of level costs you a drop from every single roll.
Step three, strips, counted wall by wall. This is where we changed our mind. We used to divide the total perimeter by the roll width. That is wrong, because you cannot wrap a full-width strip around an inside corner: you cut it, turn the corner with an inch or so, and start a fresh plumb strip on the next wall. So a 12/10/12/10 ft room needs 8+6+8+6 = 28 strips, not the 26 you get from dividing 44 ft by 20.5 inches. Two strips is a whole roll on a patterned paper. Enter your walls separated by commas and we count them properly; enter one number and we treat it as a single uninterrupted run.
Step four, the buffer. Applied to the strip count, then converted to rolls. Applying it to strips rather than to the final roll count matters: adding 10% to 4 rolls gives 4.4, which rounds to 5, a real 25% increase. Adding 10% to the 28 strips those rolls are cut from is a true 10%. The default is 10%, which is what Rochelle works to. The repeat waste is already counted in step one, so this buffer is only for miscuts, a damaged strip, a wall out of plumb, and one usable length kept back for a future repair. It is not a second helping of repeat waste, which is why the 15% that many calculators default to is more than most jobs need.
We used to. You entered a door count and a window count, we assumed 21 and 15 square feet, and we subtracted whole rolls of coverage. We removed it on 28 August 2026, because it was the most dangerous thing on this site.
Two reasons. First, the trade does not deduct openings unless one runs the full height and full width of a wall, because the strip beside a door is still a full-height cut and the piece above it has to be pattern-matched from a full drop. Second, and worse, our deduction was applied after the safety buffer, so on a room with several openings it could delete the entire buffer and then some. A 50 ft perimeter room with three doors and six windows came out at 15 bolts when the honest answer was 17: exactly enough paper if nothing at all goes wrong, on a material where re-ordering means a different dye lot.
Running out is not a rounding error, it is a ruined wall. So the openings inputs are gone. If an opening genuinely occupies a whole wall, leave that wall out of your list.
A 12 by 10 ft room with 8 ft ceilings, entered as four walls, papered in a standard US bolt of 20.5 in by 33 ft, straight match, 10.5 in repeat, buffer at the 10% default.
| Step | Arithmetic | Result |
|---|---|---|
| Cut length | 8 ft + 12 in trim = 9 ft, rounded up to a whole 10.5 in repeat: 11 × 0.875 | 9.63 ft |
| Drops per roll | 33 ÷ 9.63 = 3.43, rounded down | 3 |
| Strips, per wall | ceil(12÷1.71) + ceil(10÷1.71) × 2 pairs = 8+6+8+6 | 28 |
| Strips + 10% buffer | 28 × 1.10 = 30.8, rounded up | 31 |
| Rolls to buy | 31 ÷ 3 drops per roll, rounded up | 11 double rolls |
Eleven bolts is 620 sq ft of paper for 352 sq ft of wall. Where the rest goes: each roll yields three 9.63 ft cuts, so 28.9 ft of every 33 ft roll is used and 4.1 ft is offcut. That is 88% of each roll reaching the wall, which is about as good as patterned paper gets. The gap between 620 and 352 is not waste in the roll, it is the difference between paper bought and wall covered once you account for corners, trim and a repair length.
Enter the same room as a single 44 ft run instead and you get 10 bolts. That one-roll difference is the corner allowance, and it is the reason we ask you to list your walls.
| Preset | Dimensions | Coverage |
|---|---|---|
| US bolt (double roll) | 20.5 in × 33 ft | ~56 sq ft |
| US single roll | 20.5 in × 16.5 ft | ~28 sq ft |
| European roll | 0.53 m × 10.05 m | ~5.3 sq m |
A caution on the phrase "US standard", because it is used loosely everywhere including by us until recently. The 20.5 inch by 33 foot bolt is the most common size sold in the United States and it is what York ships on its own calculator page, but the Wallcovering Installers Association classifies that size as a metric roll and defines the historic American single roll as 34 to 36 square feet. The Wallcoverings Association agrees. There is no single US standard, and York alone ships two formats (the other is 27 inches by 27 feet). Read your own roll label; do not trust any calculator's default, including ours.
European rolls vary slightly by maker. Cole & Son specifies 0.53 m by 10.05 m, Little Greene lists 52 cm by 10.05 m, and Farrow & Ball states 53 cm by 10 m. We use 0.53 m by 10.05 m and give you a custom field for the rest.
Same strip and cut logic as wallpaper, including the repeat rounding and the match-type selector, because plenty of peel-and-stick is patterned: NextWall and NuWallpaper both publish repeats on their listings, and a 20.87 in repeat on a 16.5 ft roll is the difference between two cuts per roll and one. We used to ignore the repeat entirely on this calculator. That was wrong and it is fixed.
Two things differ from paste paper. The trimming allowance defaults to 4 inches total, 2 at each end, because peel-and-stick is precision slit and razor-trimmed in place against a smooth wall rather than sponged and cut wet. And the buffer defaults to 10%, because a strip can usually be lifted and repositioned rather than binned. Both are inputs, so change them if your material or your walls say otherwise.
Drops per roll is the roll length divided by the cut length, rounded down. Strips are the wall width divided by the roll width, rounded up. Buffer is applied to strips, as everywhere else.
Our presets are 20.5 inches by 18 feet (30.75 sq ft), which is the dominant US size across NextWall, NuWallpaper and RoomMates, and 20.5 inches by 16.5 feet (28 sq ft), which is Tempaper's single roll. Panel-format brands exist and are different animals: Chasing Paper sells 2 by 4, 2 by 8 and 2 by 12 foot panels. Use the custom field for those.
Identical arithmetic to peel-and-stick minus the pattern repeat, because grasscloth is a free match with no pattern to align. The buffer defaults to 15% rather than 10%, because grasscloth is a natural fibre with visible shading variation, there is no pattern to disguise a seam, and you want spare material from the same dye lot.
The trimming allowance defaults to 4 inches total, 2 at each end, which is what grasscloth hanging instructions specify rather than the 6 inches per end we use on paste paper. On a 10 ft ceiling that single difference is the gap between two drops and three from a 10 m bolt, which is three bolts on a large room and several hundred dollars. It is an input, so you can change it.
The American bolt is 36 inches by 24 feet, which is 8 yards and about 72 square feet, and it is sold and priced as a double roll rather than a single. That is confirmed on York's own product spec, on Grasscloth & More and at Home Depot. The metric preset is 0.91 m by 10 m, per Eurowalls, though shorter 5 m rolls also exist.
Panels are counted in a grid rather than in strips, because they are rigid and butt together rather than overlapping.
Panels across is your wall width divided by the panel width, rounded up. Rows is your wall height divided by the panel height, rounded up, after subtracting a 3 inch tolerance. That tolerance exists because a wall that is two or three inches taller than one panel does not need a second row; it needs a strip of trim or a shadow gap at the ceiling, which is what installers actually do. Without the tolerance the calculator would double your order over three inches of wall.
Total is panels across times rows, plus the buffer for miscuts. If the result needs more than one row, the calculator warns you to plan a horizontal seam, because that seam is a design decision you want to make deliberately rather than discover halfway up the wall.
The tolerance used to be silent, which was a defect: a 94.5 in panel on a standard 96 in wall leaves an inch and a half of bare drywall running the full width, and the tool cheerfully reported the wall as covered. It now tells you exactly how far short the panels finish and roughly how many linear feet of filler trim, shadow gap or top rail you need to close it. That trim is a separate purchase and nobody should discover it on installation day.
Presets are 24 by 94.5 inches for a full panel and 24 by 48 inches for a half, both verified against current listings at Home Depot and Wayfair. Note that panels are usually sold in packs of two, so an odd panel count means buying a spare. Narrow panels around 12.6 inches wide are also common; use the custom field.
Area-based, like tile, because these panels are cut to fit and the offcuts are usable. Wall area, plus a waste allowance, divided by the coverage of one panel, rounded up. The arithmetic is the easy part. The input that matters is the coverage figure, and it is the one almost everybody gets wrong.
Nominal size is not coverage. These panels are sold as 2 × 4 foot and the category pages say "24″ x 48″ overall size. Coverage varies." On a standard square-edged panel the coverage dimensions equal the overall dimensions, so Historic Brick measures 47½ × 23½ in and covers all 7.80 sq ft of it. On an interlock panel the edges overlap to hide the seam, so Stacked Stone is 47 in long and covers 41½ in of wall, or 6.70 sq ft.
Across the designs we checked, coverage runs from 6.70 to 7.80 sq ft per panel. That is a 14% spread, and there is no single site-wide constant to fall back on: the figure is published per product. On a 96 sq ft wall at a 10% allowance it is the difference between 14 panels and 16. So our calculator asks which design you have chosen rather than assuming one, and gives you a field to type the number off your own product page.
This is also why the manufacturer's own Material Needs Calculator carries the disclaimer that "as our panels vary in size and design, our calculator is an approximation." It offers a binary standard-or-interlock choice and no product selection, so it cannot use the real figure. It is a reasonable first pass; it is not the number to order from. Read the coverage off the page for the design you are actually buying.
Corners. Corner pieces are 48 in tall, so a wall taller than 4 ft needs more than one per corner: we take the wall height divided by 4, rounded up, times the number of corners. We do not deduct the wall area a corner piece covers, which is conservative by roughly 3.2 sq ft per piece. Corner prices vary by design ($52.95 to $102.95 on the range we checked) so we give you a count and leave the pricing to your order.
Adhesive. One tube per five panels and one per ten corners, which is the manufacturer's own stated ratio. Worth knowing that these panels go up with construction adhesive and screws, in every joint, and that joints and screw holes are then caulked.
Cost. Panel pricing is public and tiered: $99.95 each for 1 to 24, $95.95 for 25 to 149, and a custom quote at 150 and above. We apply the tier your count lands in and add $13.25 per panel if you tick fire-rated. At 150+ we show no price at all, because a quoted tier is not something to guess at.
What it does not do. It does not deduct doors and windows, for the same reason the tile calculator does not: on a job this size the allowance absorbs small openings, and a large opening should come out of your wall measurement before you start. It does not count ledgers, molding or columns, which are sold per piece with their own coverage figures. And it assumes a solid backing, which the manufacturer requires and which is a wall-prep question rather than a quantity one.
This one counts boards, not panels. Battens are always gaps plus one, because a batten sits at each end of the wall.
The number that matters is the clear gap between battens, not the centre-to-centre spacing, because the clear gap is what you see and what you are copying off a photograph. Those are not the same thing, and ignoring the batten width is how a layout that was supposed to read as 16 inches comes out at 12. We solve for the gap properly: from width = gaps × clear + (gaps+1) × battenWidth, the closest whole number of gaps is round((width - battenWidth) / (clear + battenWidth)). Enter the actual width of your board (a 1×4 is 3.5 inches, not 4) and we report the clear gap the layout really produces, plus the centre-to-centre figure for marking out. If the wall cannot divide near what you asked for, we say so rather than quietly handing you a different number.
Material is battens times their height, plus twice the wall width for the top and bottom rails, plus the buffer. But linear feet is not a shopping list: you cannot buy 71 linear feet, and a 3 ft offcut from an 8 ft board is scrap if every batten is 5 ft. So tell us the board length your merchant stocks and we work out how many battens come out of one board, how many boards each rail needs, and the total to put in the trolley. If your battens are longer than the stock you named, we say that instead of pretending.
Material is battens times their height, plus twice the wall width for the top and bottom rails, plus the buffer. The result is linear feet of 1× board.
Tile is the only genuinely area-based calculation here, because tiles are small relative to the wall and cuts are made from offcuts. Wall area times the waste allowance, divided by the coverage of one box, rounded up.
Box coverage presets are 12.5 sq ft for a 3 by 6 inch subway box (100 pieces, consistent across Daltile at Home Depot and American Olean at Lowe's), 16 sq ft for a 12 by 24 inch large-format box (8 pieces at 2 sq ft each), and 0.98 sq ft for a nominal 12 inch mosaic sheet, which sits inside the real observed range of 0.96 to 1.05. Boutique and imported lines ship much smaller cartons, some under 6 sq ft, so read the box.
The waste allowance now moves with the tile rather than sitting at a flat 10%: 8% for large format, where few tiles are cut and each cut is cheap; 10% for subway; 15% for mosaic sheets, which cut, break and lose pieces around outlets far more than whole tiles do. Add 5 to 10 points on top for a diagonal or herringbone lay, where nearly every perimeter tile is cut. All of it is adjustable.
Two things the calculator does not do for you. It does not add a spare box for future repairs, and you should buy one, because tile is fired in batches and a replacement bought in two years will not match. And it works from one total area, so five separate 4 ft walls totalling 40 sq ft get the same answer as one 10 ft wall of 40 sq ft, when the five walls actually generate five times the edge cuts. If your job is a lot of small faces, push the allowance up.
They do not know about your wall. Sloped ceilings, stairwells, chimney breasts, arches, dormers and anything that is not a flat rectangle need a person, and usually need each face measured separately and added together.
They do not centre a pattern for you. Where the first strip lands decides where the pattern falls at the corners and either side of a fireplace, and that is a decision, not a calculation.
They do not account for a paper hung on the horizontal, for panelled or railroaded grasscloth, or for a mural sold as a fixed set of numbered panels. Murals are sized by the manufacturer to your wall; do not estimate them.
They do not tell you whether your wall is sound. Estimating quantity is the easy half. Whether the surface needs lining paper, a size coat, or filling and sanding first is the half that decides how the job looks, and it needs an eye on the actual wall.
And they are estimates. Buy from a single dye lot, order it all at once, and check the roll label against the numbers above before you pay.
Corrections are recorded here with the date and the reason, because a calculator that changes silently is one you cannot trust.
| Date | Change | Why |
|---|---|---|
| 28 Aug 2026 | Grasscloth bolt preset corrected from 36 in × 12 ft to 36 in × 24 ft | The American bolt is 8 yards and about 72 sq ft, not 36. The old figure was half a bolt and over-ordered by roughly double. |
| 28 Aug 2026 | Peel-and-stick presets corrected from 24 in × 9 ft and 24 in × 18 ft to 20.5 in × 18 ft and 20.5 in × 16.5 ft | We could not find a 24 in × 9 ft roll on sale anywhere. The dominant US size is 20.5 in wide. |
| 28 Aug 2026 | Subway tile box coverage corrected from 10.5 to 12.5 sq ft; large format from 15.5 to 16 sq ft | Checked against current Home Depot and Lowe's cartons. |
| 28 Aug 2026 | Added a 12 inch trimming allowance (6 in at each end) to the wallpaper, peel-and-stick and grasscloth drop calculations | The drop method includes trim at the ceiling and skirting. Omitting it under-ordered on tall walls. 6 inches per end is what our reviewer cuts and matches the top of published trade guidance. |
| 28 Aug 2026 | Wallpaper waste buffer default lowered from 15% to 10% | The repeat waste is already counted in the drop height, so 15% was double-counting. 10% is what our reviewer works to. Grasscloth stays at 15% for dye-lot blending. |
| 28 Aug 2026 | Removed the doors and windows deduction from the wallpaper calculator | The trade does not deduct openings unless they fill a whole wall, and ours was applied after the safety buffer, so it could wipe the buffer out and under-order. This was the most serious fault we found. |
| 28 Aug 2026 | Wallpaper strips are now counted wall by wall instead of from a single perimeter | A strip cannot be wrapped around an inside corner. The perimeter method under-counted by roughly one strip per corner, which is a whole roll on a patterned paper. |
| 28 Aug 2026 | Pattern repeat is now rounded up to a whole repeat instead of simply added, and a match-type selector was added | Adding a full repeat to every drop is always safe and usually too much. Rounding is the actual trade rule. Half-drop matches now get their extra half repeat; random matches are no longer charged for waste they do not have. |
| 28 Aug 2026 | Wallpaper waste buffer default lowered from 15% to 10% | The repeat waste is already counted in the cut length, so 15% was double-counting. 10% is what our reviewer works to. Grasscloth stays at 15% for dye-lot blending. |
| 28 Aug 2026 | Trim allowance is now an input, and defaults per material: 12 in for paste wallpaper, 4 in for peel-and-stick and grasscloth | Grasscloth and peel-and-stick hanging instructions specify 2 in per end. Applying the paste-paper allowance to them over-ordered by up to 40% on tall walls. |
| 28 Aug 2026 | Peel-and-stick now accounts for pattern repeat | It previously ignored it entirely. Patterned removable wallpaper is common and a 20 in repeat can halve the drops you get from a roll. |
| 28 Aug 2026 | Wood slat panels now disclose the shortfall when the 3 in tolerance is used, and quantify the filler trim | A 94.5 in panel on a 96 in wall leaves bare drywall. The tool used to report the wall as covered. |
| 28 Aug 2026 | Wainscoting now solves for the clear gap using your batten width, and outputs a board count | Reporting centre-to-centre spacing as though it were the visible gap was wrong by around 24% on a typical layout, and linear feet is not something you can buy. |
| 28 Aug 2026 | Tile waste defaults now vary by tile type (8/10/15%) | A flat 10% is too low for mosaic sheets and too high for large format. |
| 28 Aug 2026 | Fixed a crash in the wood slat calculator | It wrote to a page element that does not exist, throwing on every keystroke and killing every line of output below the panel count. The detail line under the result had never rendered. Found by a headless test that runs the real page, not by reading the code. |
| 28 Aug 2026 | Added the faux stone, brick and wood panel calculator | Built around per-design coverage (6.70–7.80 sq ft) rather than the nominal 2 × 4 ft size, because that 14% spread is two panels on an average wall. Also counts corner pieces, adhesive tubes and the tiered panel cost. |
| 28 Aug 2026 | This page published | Every formula on the site is now checkable. |
Next: run the wallpaper calculator, or read who reviews these guides.