What to measure
How to use the wallpaper calculator
- Enter the room’s length and width and the wall height.
- Enter the number of doors.
- Copy the roll width and length from the label, and the pattern repeat (0 for a random match). The defaults are a common size: Brewster lists 20.5 in × 33 ft rolls, about 56.4 sq ft each.
- Keep the 4 in trim allowance for cutting at the ceiling and baseboard.
For a single accent wall, enter its width as the length and 0 as the width.
The formula
- Strips = (room perimeter − 3 ft per door) ÷ roll width, rounded up
- Strip length = wall height + pattern repeat + trim
- Strips per roll = roll length ÷ strip length, rounded down
- Rolls = strips ÷ strips per roll, rounded up
Worked example: 12 × 12 ft room, 8 ft walls, one door
- Wall run: 2 × (12 + 12) − 3 = 45 ft = 540 in; ÷ 20.5 in = 26.3 → 27 strips
- Strip: 96 in + 0 repeat + 4 in trim = 100 in (8 ft 4 in)
- Per roll: 396 in ÷ 100 in = 3.96 → 3 strips
- Rolls: 27 ÷ 3 = 9 rolls; at $45 a roll, $405
Rolls for common rooms
20.5 in × 33 ft rolls, one door, random match. Walls from 8 to 10 ft high all get 3 strips per roll, so the count is the same.
| Room | Strips | Rolls |
|---|---|---|
| 10 × 10 ft | 22 | 8 |
| 12 × 12 ft | 27 | 9 |
| 12 × 14 ft | 29 | 10 |
| 14 × 16 ft | 34 | 12 |
| 16 × 20 ft | 41 | 14 |
Frequently asked questions
How many rolls of wallpaper do I need for a 12 × 12 room?
9 rolls of 20.5 in × 33 ft for 8 ft walls with one door and a random-match pattern. The room needs 27 full-height strips, and each roll gives 3.
How does a pattern repeat change the number of rolls?
Each strip has to start at the same point in the pattern, so it uses one extra repeat. With 9 ft walls and a 24 in repeat, a 33 ft roll gives only 2 strips instead of 3, and the 12 × 12 room needs 14 rolls instead of 9.
Should I subtract windows and doors?
Subtract doors, since nothing goes above most of their width. Don't subtract windows; the short pieces above and below a window use most of a strip anyway. The calculator skips 3 ft per door and none for windows.
Why count strips instead of square feet?
Wallpaper comes in fixed-width strips cut to wall height, and leftovers shorter than a wall are rarely usable. Dividing the wall area by the roll's square footage ignores that waste and usually comes up short, especially with tall walls or a large repeat.
Is wallpaper sold in single or double rolls?
Both, and prices are often quoted per single roll even when only double rolls are sold. Enter the length of the roll you'll actually buy, from the label, and compare prices per foot.
How much extra wallpaper should I buy?
The strip count already covers trimming and pattern matching. Buy all the rolls from the same batch (printed on the label) so the color matches, and consider one spare roll for repairs, since a later batch may differ.
Sources
Formulas and defaults last reviewed October 30, 2026. How we check our math.