Why wallpaper is counted in strips
Wallpaper comes in rolls of fixed width and length, and each strip has to run from ceiling to baseboard in one piece. The leftover at the end of each roll is often too short for another full strip. That is why dividing the wall area by the roll area almost always underestimates the number of rolls. This calculator counts strips the way an installer does.
The method
- Wall run = room perimeter − total width of doors and windows.
- Strips = wall run ÷ roll width, rounded up.
- Strip length = wall height + 4 in for trimming, rounded up to a multiple of the pattern repeat.
- Strips per roll = roll length ÷ strip length, rounded down.
- Rolls = strips ÷ strips per roll, rounded up.
Worked example: a 12 × 10 ft bedroom
The walls are 8 ft high. The door and window take 6 ft of width. The paper is a random match, sold in rolls of 20.5 in × 33 ft.
- Wall run: 2 × (12 + 10) − 6 = 38 ft.
- Strips: 38 × 12 ÷ 20.5 = 22.2, so 23 strips.
- Strip length: 96 + 4 = 100 in.
- Strips per roll: 396 ÷ 100 = 3.96, so 3 strips.
- Rolls: 23 ÷ 3 = 7.7, so 8 rolls, or $400 at $50 a roll.
Rolls by wall height
| Wall height | Strips per roll | Rolls |
|---|---|---|
| 7 ft | 4 | 6 |
| 8 ft | 3 | 8 |
| 10 ft | 3 | 8 |
| 12 ft | 2 | 12 |
The number of rolls jumps in steps, not smoothly: as long as three strips fit in a roll, a taller wall costs nothing extra, then the order jumps by half. A pattern repeat has the same effect, because it lengthens each strip to a multiple of the repeat. With a 34 in repeat on 8 ft walls, each strip becomes 102 in, which still leaves 3 strips per roll; with a 70 in repeat, each strip becomes 140 in and only 2 fit. Try your own repeat before choosing a paper.
Straight and drop match
With a straight match, the pattern lines up horizontally across strips. With a drop match (half-drop), every other strip is shifted by half a repeat, which can add waste on short walls. The calculator’s method covers both, because each strip still has to start at a matching point.
Tips for ordering
- Buy one batch: the batch or lot number is printed on the label. Rolls from different runs can differ slightly in shade.
- Keep a spare roll for repairs and miscuts.
- Measure each wall: in older homes, ceiling heights vary. Use the tallest height.
- Small openings do not count: above and below a small window, you still need strips, so only deduct openings that are at least as wide as a strip.
Sizes vary by market
Many US papers come as double rolls of about 33 ft. European rolls are usually 0.53 × 10.05 m, about 20.9 in × 33 ft. Wide non-woven papers can be 27 in or more. Always enter the size on the label.