Wallpaper is not poured or spread: it is hung in strips that run from the ceiling line to the baseboard, each cut to the full height of the wall. That one fact is why the usual shortcut goes wrong.
Wall run = 2 × (room length + room width)
Drops = wall run ÷ roll width, rounded up
Drop length = wall height + trim, rounded up to a whole pattern repeat
Drops per roll = roll length ÷ drop length, rounded down
Rolls = drops ÷ drops per roll, rounded up
A 12 × 10 ft room with 8 ft walls
The walls run 44 ft around the room. The roll is 20½ in wide, so the wall needs 26 drops. Each drop is the 8 ft wall height plus 4 in of trim, which comes to 100 in; with a 12 in straight-match repeat that rounds up to 9 ft. A 33 ft roll supplies 3 of those, because the leftover length is not enough for a fourth. The rolls are then 26 drops ÷ 3 per roll = 8.67 rolls.
This example assumes
- 20½ in × 33 ft rolls, a 12 in straight-match repeat and 4 in trim, all example values: take your paper’s from its label
- Doors and windows are not subtracted
Worked example 12 × 10 ft room, 8 ft walls, 20½ in × 33 ft rolls, 12 in repeat, 4 in trim
| Material | Calculated | Buy |
|---|---|---|
| Wallpaper rolls20.5 in × 33 ft rolls, 12 in straight-match repeat, 4 in trim | 26 drops ÷ 3 per roll = 8.67 rolls | 9 rolls |
Why not wall area ÷ roll area
The walls are 352 sq ft and one roll is about 56.4 sq ft, so dividing the areas says 7 rolls. The drop method says 9 rolls. The area method treats the paper as if it could be cut into any shape, but each roll yields only whole drops, and the part of a roll shorter than one drop is unusable. Here the last 6 ft of every roll is too short for another drop and goes unused, which area division cannot see.
Doors and windows
The planner does not subtract them. A drop above a door or below a window is still cut from a full-height piece, so an opening seldom saves a whole drop. If you know how you will cut around an opening, adjust the result yourself.
What it handles
It handles a paper with no repeat (including a free or random match) and a straight match. Half-drop and offset matches are not modeled, so treat the count as a starting point for such papers and follow the paper’s instructions. The pattern repeat page shows how the repeat changes the answer. To get the wall height and run right first, see how to measure a room.
What changes the estimate?
- Roll width and length, from the roll label
- The pattern repeat, and whether the match is straight
- Trim allowance per drop, if your instructions give one
- Ceiling height, which sets the drop length