Why count strips instead of square feet
Wallpaper is hung in vertical strips, each a little taller than the wall so it can be trimmed at the ceiling and the floor. Pieces left at the end of a roll that are too short for a full strip are mostly wasted, and a pattern that has to line up from strip to strip wastes more. Counting how many full strips each roll gives, rather than dividing square feet, gives a far more reliable answer.
How the calculation works
Wall width to cover = 2 × (length + width) − 3 ft for each door
Strips needed = wall width in inches ÷ roll width, rounded up
Strip length = wall height + 4 in for trimming, rounded up to a whole number of pattern repeats
Strips per roll = roll length ÷ strip length, rounded down
Rolls = strips needed ÷ strips per roll, rounded up
In the example above, a 12 × 14 ft room has 52 feet of wall, or 49 feet after one door. That needs 29 strips of 20.5 inch paper. Each strip is 100 inches long (96 inches of wall plus 4 for trimming), so a 33 ft roll gives 3 full strips, and you need 10 rolls.
Windows are not subtracted: you still need paper above and below them, and the short offcuts from each roll usually cover those spots.
Double rolls, single rolls and pattern repeat
- Double rolls. Most wallpaper in the US is sold in double rolls of about 20.5 inches by 33 feet, roughly 56 square feet. Some retailers quote the price per single roll but only sell double rolls, so check what one "roll" means before you compare prices.
- Other sizes. European and designer papers are often about 21 inches by 33 feet, and some wide papers are 27 inches or more. Enter the size printed on the label.
- Pattern repeat. This is the vertical distance before the design repeats. A large repeat means more waste per strip, because each strip has to start at the same point in the pattern.
Tips before you buy
- Buy all the rolls at once and check that they share the same batch or dye lot number. Colors can differ slightly between batches.
- Buy one extra roll if the paper is expensive or might be discontinued, so you can repair damage later.
- For an accent wall, enter its width as the length and 0 as the width, and set doors to 0.
Frequently asked questions
How many rolls of wallpaper do I need for a 12 × 12 room?
With 8 ft walls, one door and standard 20.5 inch by 33 ft double rolls of plain paper, you need 27 strips and 9 rolls.
How many strips are in a roll of wallpaper?
For 8 ft walls, a 33 ft double roll gives 3 full strips once you allow for trimming. With a large pattern repeat, the strips get longer, and you may still get only 3 or even fewer.
How much does a double roll of wallpaper cover?
About 56 square feet of paper. Because of trimming and pattern matching, the usable coverage on a wall is typically lower, which is why this calculator counts strips instead.
Should I subtract windows?
Subtract doors, which interrupt full-height strips, but not windows. The paper above and below windows uses up the offcuts that would otherwise be wasted.
This calculator gives an estimate for buying materials. Some papers come with their own coverage chart from the manufacturer, which you should follow.