How it is calculated
Wallpaper is counted in strips, not square feet. The calculator takes the length of wall to cover (perimeter minus doors), divides it by the roll width to get strips, then counts how many full strips fit on one roll at your wall height plus 4 in for trimming. The pattern repeat makes every strip longer. Windows are not subtracted because their offcuts go above and below them.
Strips = (perimeter − doors × 3 ft) ÷ roll widthStrips per roll = roll length ÷ (height + 4 in, rounded up to the repeat)Rolls = strips × (1 + extra) ÷ strips per rollExample
A 12 × 10 ft room with 8 ft ceilings and one door needs 24 strips 20.5 in wide. A 33 ft double roll gives three strips of 8.3 ft, so with 5 % extra you need 9 double rolls.
Tips from practice
- Check that every roll has the same batch (dye lot) number.
- A large repeat (over 12 in) can add one or two rolls to a room. Always enter it.
- Keep one roll for repairs; unopened rolls can often be returned.
Questions and answers
What is a double roll?
In the US wallpaper is priced by the single roll but sold in double rolls, usually 20.5 in wide and 33 ft long, about 56 sq ft.
What is a pattern repeat?
The vertical distance after which the pattern repeats. It is on the label, for example 21 in. Each strip must start at the same point in the pattern, so some length is lost.
How many rolls for a 12 × 12 room?
With 8 ft ceilings and a small repeat, about 9–10 double rolls.
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