Wallpaper Calculator
A wallpaper calculator divides wall area by 25 usable sq ft per roll: 40 × 8 ft of wall needs 13 rolls, or 15 rolls once you add 10% for pattern matching.
Wallpaper calculator formula
A wallpaper calculator turns the area of your walls into a number of rolls. Rolls = wall area ÷ 25, rounded up. The 25 is the usable square feet per roll after trimming and pattern matching. A checkbox adds 10 percent for extra waste before the rounding.
The formula in plain words
Measure all the wall you plan to cover. Multiply the total length of the walls by their height. Divide by 25 and round up to a whole roll. If you tick the waste box, multiply the area by 1.1 first.
Worked examples
These match the calculator exactly.
- Bedroom with 40 ft of wall at 8 ft high, $45 per roll
- Area: 40 × 8 = 320 sq ft
- Rolls: 320 ÷ 25 = 12.8, rounded up to 13
- Cost: 13 × $45 = $585
- With 10% extra: 352 sq ft ÷ 25 = 14.08, rounded up to 15 rolls, $675
- A 14 × 12 ft room with 8 ft walls
- Total wall length: 2 × (14 + 12) = 52 ft
- Area: 52 × 8 = 416 sq ft
- Rolls: 416 ÷ 25 = 16.64, rounded up to 17, $765
- With 10% extra: 457.6 sq ft ÷ 25 = 18.3, rounded up to 19 rolls, $855
The waste option costs two rolls in both examples. For a small room that is a real cost, but running out half way is worse.
Rolls by wall area
| Wall area | Rolls at 25 sq ft | With 10% extra |
|---|---|---|
| 100 sq ft | 4 | 5 |
| 200 sq ft | 8 | 9 |
| 320 sq ft | 13 | 15 |
| 416 sq ft | 17 | 19 |
| 600 sq ft | 24 | 27 |
Pattern repeat and waste
A plain or small pattern wastes less than a large one. With a large repeat, each strip must be cut so the design lines up with its neighbor, and that leaves offcuts. The bigger the repeat, the more paper you lose. If your pattern repeats every 24 inches or more, the 10 percent allowance is a sensible minimum. Look at the repeat on the label before you buy.
Some papers, such as a random match or a plain textured sheet, waste very little. If your paper is one of these and the label says so, you may not need the extra.
How to measure
Measure each wall from the baseboard to the ceiling and add the widths. For a room, add all four walls. If you only paper one accent wall, measure that wall. For a gable or stair wall, measure the highest and lowest points, and use the average. Round up the measurement to the next inch, then round up the total.
The tool asks for a length and a width, so enter the total length of the walls and their height. That gives the wall area.
Preparing the walls
Fill holes and smooth bumps, and clean off dust and grease. A primer or sizing helps the paste hold and makes it easier to remove the paper later. Follow the paper maker’s instructions on paste, soaking time and trimming. Cut each strip a few inches longer than the wall height, hang it, and trim the extra after.
Wallpaper cost
The tool multiplies whole rolls by the price per roll, with $45 as a placeholder. Some papers are sold by the double roll, which holds two single rolls. If so, divide your roll count by 2 and round up, and enter the double roll price per piece. Paste, a primer and tools are extra.
Doors, windows and accents
If you leave out a door, the usual rule is to subtract its area, about 20 sq ft. For example 1 that cuts the area to 300, or 12 rolls instead of 13. Keep the waste allowance, since you still cut around the frame. A single accent wall that is 12 ft wide and 8 ft high is 96 sq ft, or 4 rolls without waste.
Common mistakes
- Using the roll’s printed coverage as usable coverage.
- Forgetting the pattern repeat.
- Buying rolls from different batches.
- Subtracting too much for windows and doors.
- Not rounding up.
Related pages
For wall paint, see the paint calculator. Prime first with the primer calculator. For board on the walls, see the drywall calculator.
Frequently asked questions
How many rolls of wallpaper do I need?
Find the wall area, divide by the usable area per roll, and round up. The tool uses 25 sq ft per roll. A room with 40 ft of wall at 8 ft high is 320 sq ft, or 12.8 rolls, which rounds up to 13.
Why does the tool use 25 sq ft per roll?
A roll lists more area than you can use, because you lose some to trimming and to lining up the pattern. 25 usable square feet is a cautious figure. Check the roll's label, and if it differs, divide by your own number.
Should I subtract windows and doors?
You can. A standard door is about 20 sq ft and a 3 × 4 ft window is 12 sq ft. If your pattern repeats a lot, subtract less, since the strips above windows and doors still use paper.
What does the 10 percent do?
It adds waste for matching a pattern, mistakes and trimming. With it on, 320 sq ft becomes 352, which is 14.08 rolls and rounds up to 15.
Should I buy all rolls at once?
Yes, buy them in one order and check that the batch numbers match. Dye lots can differ slightly, and a different batch may show a color shift on the wall.
Estimates only. Verify quantities with your supplier before purchasing.