How to use the wallpaper calculator
- List each wall with its width and height. If a wall has a full-height door or opening, enter its width so the strips that would cover it are removed.
- Enter the roll width and length from the label, or use the US or European preset and edit it. Choose whether the roll boxes are in inches and feet or centimeters and meters.
- Enter the pattern repeat and pick straight match, half-drop match or random. Leave the repeat blank for a plain paper.
- Read the number of strips, the cut length and the rolls to buy. Keep the 5% extra roll allowance or change it, then copy the shopping list.
Formula
Strips on a wall = (wall width - opening width) / roll width, rounded up
Strip length = wall height + trim allowance
Straight match: cut length = strip length rounded up to a whole number of repeats
Half-drop match: cut length = (strip length + repeat / 2) rounded up to a whole number of repeats
Rolls = all strips packed into roll lengths, longest first
Rolls to buy = rolls x (1 + extra percent / 100), rounded up
A matched pattern cannot start mid-repeat, so every strip is cut to a multiple of the repeat. That rounding is where most of the waste comes from. The packing step lets short strips from one wall share a roll with strips from another.
Worked example: a 12 by 10 foot room with an 8 foot ceiling and a 3 foot door
The roll is 20.5 inches wide and 33 feet (396 inches) long, with a 12 inch straight-match repeat and 4 inches of trim per strip.
Wall strips are 12 ft: 144 / 20.5 = 7.02, so 8 strips; 10 ft: 120 / 20.5 = 5.85, so 6 strips; and the other two walls give 8 and, with the 3 ft door removed, (120 - 36) / 20.5 = 4.10, so 5 strips. That is 27 strips in all.
Each strip is 96 + 4 = 100 inches, rounded up to the next whole repeat, which is 108 inches. A 396 inch roll yields floor(396 / 108) = 3 strips.
27 strips at 3 per roll need 9 rolls. With 5% extra, 9 x 1.05 = 9.45, so you would buy 10 rolls.
Why the pattern repeat matters
Wallpaper with a large repeat wastes more paper than a plain one. With a 12 inch repeat, a wall that needs a 100 inch strip uses 108 inches of paper, because the next strip must line up with the first. A 24 inch repeat would round the same strip up to 120 inches. The longer the repeat, the fewer strips fit on a roll, and sometimes a single extra inch of wall height drops the count by one strip per roll.
A straight match lines up across the strip at the same height. A half-drop match shifts each strip down by half a repeat, which needs extra paper. This tool adds half a repeat to every strip for the half-drop option, which is a conservative simplification. A random match or a plain paper needs no pattern rounding.
Roll sizes and double rolls
Roll sizes differ by region and brand. US papers are often sold as double rolls with a common width near 20.5 inches, while European papers are often about 53 centimeters wide and 10 meters long. Because the length you hang from a roll depends on how it is packaged, the roll boxes accept the numbers printed on the label, and the presets only give a starting size.
Sellers sometimes quote coverage in square feet per roll. That figure assumes no pattern waste, so do not substitute it for the strip method here.
Order everything together
Wallpaper is printed in batches, and color can differ a little between batches. Order every roll at once and check that the batch numbers match. Keep a spare roll for repairs, which is the main reason this tool defaults to a 5% allowance that rounds up.
Assumptions and limits
- Strips are counted wall by wall and rounded up. This ignores the small savings from wrapping a strip around a corner.
- Windows are not deducted. Only full-height openings that you enter reduce the strip count.
- Half-drop adds half a repeat to every strip, which may slightly overestimate.
- Trim allowance and roll size are inputs. Product labels and installation instructions come first.
- Paste, primer, lining paper, seam rollers and labor are not included.
- Sloped ceilings, gables, stairwells and curved walls need hand measuring of each strip.
Frequently asked questions
How many rolls of wallpaper do I need for a room?
Count the strips needed to cover the walls, work out how many cut strips fit on one roll, and divide. The tool does this wall by wall and rounds up to whole rolls.
What is a pattern repeat?
It is the vertical distance before the design repeats itself. You need to cut each strip to a multiple of it so neighboring strips match.
What is the difference between a straight match and a half-drop match?
A straight match puts the pattern at the same height on neighboring strips, while a half-drop match offsets each strip by half a repeat. The offset uses more paper.
Should I buy extra wallpaper?
Most people buy at least one spare roll because of mistakes, pattern waste and future repairs. The extra percentage rounds up to a whole roll.
Do I subtract windows from the wallpaper estimate?
This tool does not, because the paper above and below a window still needs a full strip and the offcuts are often not usable. Only full-height doors and openings are removed.