About this tool
Wallpaper Calculator is a free, in-browser tool that estimates how many rolls of wallpaper a room needs. Give it the room size (as a perimeter, or a length and width it converts to a perimeter), the wall height, your roll's width and length, the pattern repeat, and how many doors and windows to deduct. It works in metres or feet, and everything is computed locally as you type.
The number of vertical strips (drops) around the room is the perimeter divided by the roll width, rounded up. Each drop is cut to a whole number of pattern repeats so the design lines up, giving an effective drop length of ⌈height ÷ repeat⌉ × repeat; the number of full drops you get from one roll is the roll length divided by that effective drop, rounded down. Openings reduce the drop count, a waste allowance is added, and the rolls needed is the adjusted drop count divided by drops-per-roll, rounded up.
Unlike a plain paint calculator, this accounts for the pattern repeat — the single biggest driver of wallpaper waste — and for the fact that partial drops from doors and windows rarely reuse cleanly. It also reports the net wall area after openings so you can sanity-check against a roll's stated coverage. Buy from the same batch and keep a spare roll for repairs.
Frequently asked questions
Why does the pattern repeat increase the number of rolls?
To make the design line up between strips, each drop must be cut at a whole number of pattern repeats, so a drop is rounded up to the next repeat. That extra trim at the top of every strip is waste, which means fewer usable drops per roll and more rolls overall. A repeat of 0 (a plain or random match) avoids this.
How are doors and windows handled?
Each door and window is deducted using a standard opening size (about 1.9 m² per door and 1.4 m² per window, or 21 ft² and 15 ft²). The tool converts that saved area into whole drops it can skip, but it stays conservative because offcuts around openings often cannot be reused elsewhere.
Should I measure the perimeter or the length and width?
Either works. If you know the total distance around the room, enter the perimeter directly. Otherwise switch to length × width and the tool computes the perimeter as 2 × (length + width). Then add the wall height for the drop length.
How much waste should I allow?
The default 10% covers trimming, pattern alignment and mistakes; bold or large-repeat patterns may warrant 15–20%. The tool rounds up to whole rolls after the allowance. Order all rolls from the same batch number so the colour matches, and keep a spare — everything is calculated privately in your browser.
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