About this tool
This wallpaper calculator counts rolls the way a decorator does, by drops: it works out how many full-height strips fit around the room, how long each strip must be once the pattern repeat and trimming allowance are included, how many strips one roll yields, and therefore how many rolls to buy, with one spare recommended from the same batch. Presets cover American single and double rolls (20.5 in and 27 in wide) and European and UK rolls (53 cm and 70 cm by 10.05 m), or you can enter any custom size. Doors and windows are deducted in a quick area-based estimate shown alongside so you can see how much the simple method under-orders, and a paste estimate and price per roll round out the shopping list. It is for anyone papering a room, feature wall, or hallway, in feet and inches or meters and centimeters.
How it works
Drops = perimeter / roll width, rounded up, because every strip must run the full wall height. Drop length = wall height + trim allowance, and when the paper has a pattern repeat the length is rounded up to a whole number of repeats (ceil(height / repeat) x repeat) so every strip can be aligned; a half-drop match adds a further half repeat to the cut length. Drops per roll = floor(roll length / drop length), and rolls = ceil(drops / drops per roll). With a 48 ft perimeter, 8 ft walls, and a US single roll of 20.5 in x 16.5 ft, that is 576 / 20.5 = 28.1, so 29 drops; 198 in / 96 in = 2 drops per roll; 29 / 2 = 14.5, so 15 rolls. The area check divides the wall area, less doors and windows and plus a waste percentage, by the roll's nominal area (28 sq ft for a US single roll). Paste is estimated from the gross wall area at a coverage you can edit (300 sq ft per gallon of premixed adhesive by default).
Frequently asked questions
How many rolls of wallpaper do I need for a 12 by 14 foot room?
A 12 x 14 ft room has a 52 ft perimeter. With 8 ft walls and US single rolls (20.5 in wide, 16.5 ft long) that is 624 in / 20.5 in = 31 drops; each drop is 96 in plus trim, so a roll yields 2 drops, and you need 16 rolls (8 double rolls) for a paper with no pattern repeat. A 21-inch repeat pushes each drop to 105 in, one per single roll, so the count roughly doubles; European 53 cm x 10 m rolls yield 4 drops each, so the same room needs about 8 of them.
Should I subtract doors and windows?
In the drop method, usually not. The strip above a door or around a window is a partial drop cut from the roll, and the piece you save is rarely a full drop, so most decorators count every drop around the room and use the offcuts for the short pieces. The calculator lets you deduct one drop for each door wider than the roll if you want a tighter count. The area method does subtract openings, which is one reason it tends to under-order on patterned paper.
What does pattern repeat mean and why does it matter?
The repeat is the vertical distance before the pattern starts again, printed on the label (for example 21 in or 53 cm). To match the pattern across strips each drop has to start at the same point in the repeat, so drops are cut in whole repeats and the excess is trimmed. A straight match uses ceil(height / repeat) x repeat per drop; a half-drop (offset) match needs about an extra half repeat, because alternate strips shift by half a repeat. Free-match and plain papers have no repeat and waste the least.
Why buy an extra roll?
Wallpaper is printed in batches (dye lots), and the same design from a different batch can differ slightly in color. If you run short, or damage a strip years later, a roll from the original batch is the only guaranteed match. Most retailers accept unopened rolls back, so ordering one more than the calculation and returning it later costs little. Check that every roll carries the same batch number before you start hanging.