How to calculate how much wallpaper you need
Wallpaper is figured in vertical strips, not square feet — because every strip has to run floor-to-ceiling and line up with its neighbor. Here's the method the calculator uses:
- Perimeter = 2 × (length + width) — the distance around the room.
- Strips needed = perimeter ÷ roll width, rounded up (how many drops go around the room).
- Strip drop = wall height + one pattern repeat (the extra you trim off to match the pattern).
- Strips per roll = roll length ÷ strip drop, rounded down.
- Rolls = strips needed ÷ strips per roll, rounded up.
That's why two rooms the same size can need different amounts of wallpaper: a bold, large-repeat pattern wastes more per strip than a plain or small-repeat one.
The wallpaper mistake that ruins a whole wall
Wallpaper is printed in batches (also called run or lot numbers), and the color can shift slightly from one batch to the next. If you run short and buy a "matching" roll later, it can be visibly off. Two rules the pros never break:
- Buy it all at once, and check that every roll shows the same batch number.
- Buy one extra roll from that same batch and keep it — cheap insurance for a torn corner or a future repair.
Standard wallpaper roll sizes
| Roll type | Typical size | Approx. coverage |
|---|---|---|
| Standard / "Euro" single roll | 20.5 in × 33 ft | ~56 sq ft |
| American single roll | 27 in × 13.5 ft | ~30 sq ft |
| American double roll | 27 in × 27 ft | ~60 sq ft |
| Peel-and-stick roll | varies (check label) | varies |
Roll sizes vary a lot by brand, so always enter the width and length printed on your wallpaper's label for the most accurate count.
Wallpaper calculator FAQ
- How many rolls of wallpaper do I need?
- Divide the room's perimeter by the roll width for the strips you need, and the roll length by your strip drop (wall height plus one pattern repeat) for strips per roll, then divide and round up. A typical 12 × 12 ft room with 8 ft walls and a plain pattern comes out around 8 standard rolls.
- What is a pattern repeat and why does it matter?
- It's how far up the roll the design repeats before starting again. Matching the pattern across strips wastes up to one repeat per strip, so a bigger repeat means more rolls. Enter the repeat from the roll's label.
- Should I subtract doors and windows?
- Usually no. The offcuts left over from papering around a door or window normally cover the short areas above and below them, so it's safest to figure the full walls.
- Should I buy an extra roll?
- Yes — one extra from the same batch/lot number. Colors can shift between print runs, so a roll bought later may not match.