Wallpaper Calculator
Rolls by USABLE coverage, not the gross on the label — with the pattern-repeat tax priced openly.
Wallpaper Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Rectangular rooms at fixed opening sizes.
- No strip-by-strip layout for half-drop alignment.
- No paste or liner materials.
In short: A 12 × 14 room at 9 ft, one door, one window: 432 ft² net × 1.15 ÷ 56 usable per US double roll = 9 rolls. With a +20% pattern repeat: 11.
Formula
net = 2(L+W)×H − 21/door − 15/window
rolls = ⌈net × (1 + 15% + pattern) ÷ usable⌉
usable: 28 single / 56 double / 45 Euro
priced per single, shipped per double
[('usable', 'what survives seams and trim — the honest denominator'), ('+20%', 'the straight-match repeat’s tax'), ('21 / 15', 'ft² back per door / window'), ('dye lot', 'one bolt series per room, no exceptions')]
Worked Example
- Net the walls: gross minus openings.
- Pick usable coverage by roll type — never gross.
- Add 15% trim plus the pattern chip.
- Ceil to rolls and price them.
- Order one dye lot; pack count doubles singles.
The 12 × 14 room at 9 ft: 468 gross − 36 = 432 net; 432 × 1.15 ÷ 56 = 9 double rolls ($360.00 at $40). Patterned: the +20% chip lifts it to 11. Shipped as five doubles — the single-roll price is a quotation, not a package.
Strengths & Limits Of This Model
Where this engine is strong
- Usable-vs-gross lie caught on its own card
- Pattern tax a choice, not a surprise
- Single-price/double-package trap documented
Where it stops
- Fixed opening sizes
- No strip-count layout mode
Practical Use Cases
Accent walls
One bolt, one statement, counted.
Whole rooms
Net area to rolls with repeat taxed.
Euro papers
45-ft² usable priced honestly.
Pattern shopping
The repeat’s cost before you fall in love.
Hanger bids
Roll counts against the quote.
Methodology & Editorial Standards
Net area is perimeter × height minus 21/15 ft² openings. Rolls ceiling net × (1 + 15% trim + chosen pattern chip) over USABLE coverage — 28/56/45 by roll type — never the gross on the label. The gross-vs-usable gap is printed on its own card. Price is free-entry per roll.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Wallpaper Calculator — 10 Expert FAQs
10 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How many rolls of wallpaper for a 12x14 room?
432 ft² net at 9-ft walls ÷ 56 usable per US double roll, plus 15% trim: 9 rolls. A straight-match pattern lifts it to 11 — the repeat is real paper.
What is a double roll?
Twice a single: about 72 ft² gross, 56 usable. US wallpaper is PRICED per single roll but PACKAGED in doubles — an order for 9 singles arrives as five doubles. Order by area, buy by the package.
How much wall does one roll cover?
About 28 usable ft² for a US single, 56 for a double, 45 for a Euro roll — after seams and trim. The gross numbers (36/72/57) are what the label brags.
Why does pattern matching cost paper?
Every strip must begin on the pattern, so the offcut between drops is unusable — 20% more for straight matches, 25% for drop matches. Random textures cut freely and skip the tax.
Should I deduct doors and windows?
Yes: 21 ft² per standard door, 15 per window. The cutting around them is real, but the roll rounding absorbs it — this is the deduction that works.
What is a dye lot and why does it matter?
Wallpaper prints in batches, and batches drift in tone. One room, one dye lot — order it all at once, because next month’s bolt is a different wall.
Can I wallpaper over painted drywall?
Usually, after washing and possibly sizing — glossy or failing paint needs prep. The count does not change; the paste and the hanger’s mood do.
How much extra should I keep for repairs?
One roll beyond the order, stored flat — same dye lot, future patch. Wallpaper repairs with mismatched paper look like scars.
Peel-and-stick vs paste the wall?
Peel-and-stick suits rentals and accent walls and comes in narrower panels — count by the same usable-coverage law with the panel’s own numbers. Traditional paste wins on large, permanent rooms.
How long does wallpaper last?
Decades when the wall was honest — clean, sealed, primed. It fails at seams over damp or greasy walls, not at the paper. Prep is the durability.