Wallpaper Calculator
Wallpaper Calculator: How to Work Out How Much Wallpaper You Need
Updated: Aug 2026
Working out how much wallpaper you need comes down to four steps: measure each wall, subtract the openings, divide by the roll's coverage, and add an allowance for pattern and waste. Every wallpaper calculator, including a manual one done with a tape measure and a notepad, is doing exactly this underneath — a search for "wallpaper calculator" is really a search for someone else to run these four steps for you, accurately, across every wall in the room. Here's each step spelled out, and where doing it by hand for more than one wall starts costing more time than it saves.
Open the Wallpaper PlannerStep 1: measure every wall separately, not the room as one number
Measure each wall's width and height on its own, rather than adding up a rough room perimeter and one ceiling height — a room is a set of individual walls, and treating it that way catches a sloped section, an alcove, or a taller feature wall that a single blended number would hide.
Step 2: subtract doors and windows above a minimum size
A large window or a doorway removes enough wall to skip a full strip, so subtract its width from that wall's total before working out the strip count — but a small window is often narrower than a single strip anyway, and subtracting it can undercount the strips actually needed either side of it.
Step 3: convert wall width to strips, then strips to rolls
Divide each wall's width by your roll's width to get the number of strips it needs, then divide the wall's height into the roll's length to see how many strips one roll yields — that ratio is what turns a wall's dimensions into an actual roll count, not the wall's area on its own.
Step 4: add a pattern repeat allowance before rounding up
If the paper has a repeat distance, each strip after the first needs extra length trimmed off to keep the design aligned, which lowers how many strips one roll actually yields — build that into step 3 before rounding the final roll count up, not after.
Get your exact roll count
Skip the guesswork — draw your walls and get an exact number of rolls in about two minutes.
Try the wallpaper calculator →Where doing this by hand starts to cost more time than it saves
Four steps per wall is manageable for one wall; multiplied across a whole room's worth of walls, plus a pattern repeat allowance recalculated each time, it adds up to a lot of arithmetic to get right by hand. A calculator that lets you draw the room once and runs the same four steps against every wall automatically is the point where it stops being worth doing manually.
Edge cases the four basic steps don't cover
A stairwell with a sloped run needs each stepped section measured individually rather than one blended height, since the wall height changes with every stair. A room with a ceiling above roughly 2.6m may need a horizontal join partway up if the roll's length can't cover a single strip, which changes both the drop count and how the pattern repeat lines up across the seam. Neither case fits neatly into a flat width-times-height calculation, and both are exactly where a manual estimate is most likely to go wrong.
The most common mistake: rounding down mid-calculation
Rounding a wall's strip count down instead of up — treating 4.3 strips as four rather than five — is the single most common error in a hand calculation, and it compounds across every wall in the room. Round up at the end of each wall's calculation, not at the end of the whole room, or a shortfall on one wall gets masked by surplus on another and only shows up once you're partway through hanging.
How a professional's estimate compares to a DIY figure
A decorator quoting for the job will usually order more than the bare mathematical minimum — often adding a 15-20% buffer rather than the 10% a careful DIY calculation might use — to cover hanging mistakes, pattern-matching offcuts, and the cost of a callback if they run short mid-job. That gap isn't the decorator overcharging; it's pricing in the risk of a second site visit, which a DIY job doesn't need to budget for in the same way.
Ready to see the price for your project?
Get a free roll estimate in the planner, then unlock the exact cutting plan, workbench sheets, and order list from a one-time project or yearly plan.
See plans & pricingCommon questions
Is a wallpaper calculator actually more accurate than doing the maths myself?
It's the same maths — the advantage isn't a different formula, it's applying it consistently to every wall including the ones a hand calculation is most likely to get wrong, like a sloped section or an alcove.
Does a wallpaper calculator handle pattern repeat and odd-shaped rooms?
A good one does — enter the repeat distance from the roll label and draw the room's actual shape, including sloped walls or alcoves, rather than treating every room as a flat rectangle.
Is there a cost to using a wallpaper calculator?
Getting a roll estimate is free — you'd only pay if you want the exact cutting plan, workbench sheets, and order list on top of the basic roll count.
Do I need to create an account before I can see a result?
No — draw the room and get the roll count first, with no signup required. An account only comes into play if you decide to unlock the full cutting plan afterwards.
What if my ceiling is taller than the wallpaper roll is long?
You'll need a horizontal join partway up the wall, matching the pattern across the seam. Measure the two sections separately and add extra to the repeat allowance, since a horizontal join uses more paper than one continuous vertical strip would.
Why did a decorator's roll order come out higher than my own calculation?
Professional quotes typically build in a larger buffer than a bare DIY estimate — commonly 15-20% versus 10% — to cover hanging errors and pattern-matching waste without needing a second site visit if they run short.
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Get your exact roll count
Draw your walls — including sloped sections, alcoves, and single feature walls — and get a free estimate before you buy.
Open the Wallpaper PlannerPlanning a specific room? See how much wallpaper you need →
Quoting this as a job, not a DIY project? Try the contractor estimator →
Ready to draw your own room instead of doing the maths by hand? Open the wallpaper calculator →
Setting up a small home-office feature wall? Home office wallpaper calculator →
Also need to account for pattern repeat? Wallpaper pattern repeat calculation →
Working out the cost too? Wallpaper cost calculator →
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