What the Wallpaper Roll Calculator does
This calculator works out how many rolls of wallpaper to buy by counting drops - the vertical lengths you cut and hang - rather than dividing wall area by roll area. It rounds each drop up to the pattern repeat, fits as many drops as a roll really yields, subtracts doors and windows, and cuts the short pieces above and below them from the offcuts before opening a new roll.
Counting drops is how decorators estimate, because a roll can only be cut into whole drops. The area method looks tidier but routinely falls a roll or two short on patterned paper.
How to use it
- Choose your unit and enter the wall height from skirting to ceiling.
- Add each wall's width, then add each door and window with its width and height.
- Enter the roll width and length from the label - a standard European roll is 0.53 x 10.05 m; many US rolls are about 20.5 in x 33 ft (a double roll is twice that).
- Choose the pattern match and enter the repeat from the label. Free match has no repeat; straight match lines up across every drop; half-drop shifts every other drop by half a repeat.
- Keep the trim allowance (about 10 cm per drop) and tick the spare roll, then read the rolls to buy.
Reading the results
Drops per roll is the most important number. A 10.05 m roll gives four 2.5 m drops of plain paper, but only three once a 53 cm repeat rounds each drop up to 2.65 m.
Short drops over doors and under windows are usually cut from the ends of rolls. The calculator uses offcuts first and only adds rolls when they run out.
Paper wasted shows how much of what you buy does not end up on the wall. Large repeats and tall walls push it up.
Worked example: a 14 m bedroom with a door and window
Four walls measure 4 + 3 + 4 + 3 = 14 m around and 2.4 m high. There is a 0.9 x 2.0 m door and a 1.2 x 1.2 m window. The paper is 0.53 x 10.05 m with a 53 cm straight-match repeat.
Each drop needs 2.4 m + 0.1 m trim = 2.5 m, which rounds up to 5 repeats = 2.65 m. A roll gives 10.05 / 2.65 = 3.79, so 3 drops. The width without openings is 14 - 0.9 - 1.2 = 11.9 m, needing 11.9 / 0.53 = 22.45, so 23 full drops and 23 / 3 = 7.67, so 8 rolls.
Above the door are 2 short drops of 0.53 m (0.4 m + trim, rounded to one repeat); above and below the window 3 of 1.59 m. Seven rolls end with 2.1 m spare and the eighth with 4.75 m, so all five short drops come from offcuts. With one spare roll, buy 9.
Formulas and scoring rules
- Cut length
free match: height + trim; straight match: ceil((height + trim) / repeat) x repeat; half-drop: straight-match length + repeat / 2- Drops per roll
floor(roll length / cut length)- Full drops
ceil((total wall width - opening widths) / roll width)- Short drops
for each opening: ceil(opening width / roll width) pieces, each (height - opening height) + trim, matched like a full drop- Rolls
ceil(full drops / drops per roll), plus a new roll whenever a short drop does not fit any offcut (first fit, longest first), plus the spare
Limitations: what the result does not prove
- Walls are treated as simple rectangles. Sloping ceilings, stairwells and chimney breasts need each face entered separately, and still take extra care.
- The half-drop allowance adds half a repeat to every drop, a common conservative rule; a skilled hanger working from two rolls at once can sometimes do better.
- Roll sizes vary. Check whether a US figure is for a single or a double roll, and use the manufacturer's stated usable length.
- It does not include lining paper, paste or the ceiling.
Privacy: where your data goes
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Standards and sources
Frequently asked questions
How many rolls of wallpaper do I need for a room?
Work out how many drops the walls need (width divided by roll width) and how many drops one roll gives (roll length divided by the cut length). Divide the first by the second and round up. For a typical 3.5 x 3.5 m bedroom with 2.4 m walls and a standard roll, that is usually 7-9 rolls depending on the pattern.
What is a pattern repeat?
It is the vertical distance before the design repeats itself. Each drop must start at the same point of the pattern, so drops are cut in whole multiples of the repeat. A large repeat can turn four drops per roll into three, which is why patterned paper needs more rolls.
What is the difference between straight match and half-drop?
In a straight match the pattern lines up horizontally across every drop. In a half-drop the pattern on every other drop sits half a repeat lower, so alternate drops start at a different point and waste a little more. The label shows which one your paper uses.
Should I subtract doors and windows?
Subtract their width from the full-height drops, but remember the paper above a door and above and below a window. Those short pieces are usually cut from offcuts; the calculator counts them and only adds a roll if the offcuts run out.
Why buy a spare roll?
Rolls are printed in batches whose colour can differ slightly, and a replacement bought later rarely matches. One spare from the same batch covers a mis-cut drop and later repairs.
Is the area method accurate for wallpaper?
Not reliably. Dividing wall area by roll area ignores that a roll is cut into whole drops and that the repeat lengthens each drop. It tends to under-order patterned paper; counting drops, as this calculator does, avoids that.
Last reviewed by the A2Z.Tools team against the sources listed above.
