How to calculate wallpaper
Work in strips — full vertical drops of wallpaper. First find how many strips wrap the room, then how many strips you can cut from one roll:
Strips needed = Perimeter ÷ Roll width
Strips per roll = Roll length ÷ (Wall height + pattern repeat)
Rolls = Strips needed ÷ Strips per roll
For a 40-ft perimeter, 8-ft-high room with standard 20.5-inch × 33-ft rolls and no repeat: about 24 strips, 4 strips per roll, so 6 rolls.
Wallpaper rolls for common room sizes
Rolls needed for common rooms with 8-ft walls, using a standard 20.5-inch × 33-ft roll and no pattern repeat. A larger repeat means more rolls — use the calculator to add it.
| Room size | Perimeter | Strips | Rolls |
|---|---|---|---|
| 10 × 10 ft | 40 ft | 24 | 6 |
| 12 × 12 ft | 48 ft | 29 | 8 |
| 12 × 15 ft | 54 ft | 32 | 8 |
| 15 × 20 ft | 70 ft | 41 | 11 |
Pattern repeat and waste
A pattern repeat means each strip needs up to one extra repeat length to line up, so it lowers the strips you get per roll. Always round up to whole rolls and buy one spare from the same dye lot for repairs.
Frequently asked questions
How many rolls of wallpaper do I need?
Divide the room perimeter by the roll width to find how many vertical strips you need, then divide the roll length by the wall height to see how many strips you get per roll. Divide strips needed by strips per roll and round up. For a typical 40-foot perimeter, 8-foot room with standard rolls, that is about 6 rolls.
How do I measure a room for wallpaper?
Add up the width of every wall to get the room perimeter, and measure floor to ceiling for the wall height. For ordering, most people do not subtract doors and windows — the offcuts rarely fit elsewhere, and the extra acts as a safety margin.
What is pattern repeat and why does it matter?
Pattern repeat is the vertical distance before the design repeats. To line up the pattern across strips, you waste up to one repeat per strip, so a large repeat means more wallpaper. The calculator adds the repeat to each strip's effective length.
How much extra wallpaper should I buy?
Always round up to whole rolls, and buy at least one extra roll for mistakes, future repairs, and dye-lot matching. Order all rolls in the same batch so the colors match exactly — dye lots can differ noticeably between print runs.
What size are standard wallpaper rolls?
A common European "Euro roll" is about 20.5 inches wide and 33 feet long. American rolls vary. Check your roll's dimensions and enter them, since width and length both change how many strips you get.
Disclaimer: Estimates count full walls without subtracting openings, which builds in a margin. Confirm against your wallpaper's specs and buy a little extra for matching and repairs.