What Is the Wallpaper Calculator?
The Wallpaper Calculator estimates the number of rolls needed to paper a room. It uses the strip method that professional decorators use: it counts how many vertical strips are needed to go around the room, works out how many full-height strips can be cut from one roll, and divides one by the other.
This method is more reliable than dividing wall area by roll area. Wallpaper is hung in full-height drops, and the leftover at the end of a roll is usually too short to use. Patterned papers waste even more, because each strip must be shifted so the design lines up with its neighbour. The strip method accounts for both effects.
How the Calculator Works
The calculator finds the room’s perimeter from its length and width. It subtracts 3 feet for each door, since no full-height strip is needed there. Windows are not subtracted, because paper is normally hung above and below them and the cut-outs cannot be reused.
It converts the remaining wall width to inches and divides by the roll width to get the number of strips, rounding up.
Each strip must be as long as the wall is high, plus 4 inches for trimming at the ceiling and baseboard, plus one pattern repeat to allow for matching. The calculator divides the roll length by this cut length and rounds down to get the number of usable strips per roll. Finally, it divides the strips needed by the strips per roll and rounds up.
The Wallpaper Formula
Wall width = 2 × (Length + Width) − (Doors × 3 ft)
Strips needed = Wall width (in) ÷ Roll width (in), rounded up
Cut length = Wall height + Pattern repeat + 4 in
Strips per roll = Roll length ÷ Cut length, rounded down
Rolls = Strips needed ÷ Strips per roll, rounded up
Roll sizes
A standard European roll is 20.5 inches wide and 33 feet long, covering about 56 square feet. American single rolls vary and are usually sold as double rolls, commonly 20.5 or 27 inches wide. Always use the dimensions printed on the label.
Step-by-Step Explanation
- Add the room length and width, multiply by 2, and subtract 3 feet for each door.
- Multiply by 12 to convert to inches.
- Divide by the roll width and round up for the number of strips.
- Add the wall height, the pattern repeat and 4 inches to get the cut length.
- Divide the roll length by the cut length and round down for strips per roll.
- Divide strips needed by strips per roll and round up.
Worked Example
A bedroom is 14 feet by 12 feet with 8 foot walls and one door. The paper is 20.5 inches wide and 33 feet long, with no pattern repeat.
- Perimeter: 2 × (14 + 12) = 52 feet.
- Less one door: 52 − 3 = 49 feet, or 588 inches.
- Strips: 588 ÷ 20.5 = 28.7, so 29 strips.
- Cut length: 8 feet + 4 inches = 8.33 feet.
- Strips per roll: 33 ÷ 8.33 = 3.96, so 3 strips.
- Rolls: 29 ÷ 3 = 9.7, so 10 rolls.
Now suppose the paper has a 21 inch repeat. The cut length becomes 8 + 1.75 + 0.33 = 10.08 feet. A 33 foot roll still yields 3 strips, so the answer stays at 10 rolls. With 9 foot walls and the same repeat, the cut length is 11.08 feet, each roll gives only 2 strips, and the room needs 15 rolls. Small changes in height or repeat can change the roll count sharply.
How to Use the Calculator
- Enter the room length, width and wall height.
- Enter the number of doors.
- Enter the roll width and length from the wallpaper label.
- Enter the pattern repeat. Use zero for plain, textured or random-match paper.
- Press Calculate.
- Add one spare roll to the result when you order.
For a single feature wall, enter the wall’s width as the room length and set the room width to a very small number, or simply divide the wall width in inches by the roll width. To find wall area for comparison with paint, use the Square Footage Calculator. The Paint Calculator estimates paint for the remaining walls, ceiling and trim. If walls need repair or new board first, see the Drywall Calculator, and if the floor is being replaced in the same project, the Flooring Calculator or Carpet Calculator sizes that order.
Practical Tips
- Buy all rolls with the same batch or dye lot number. Colours vary between print runs.
- Order one extra roll. It covers mistakes now and repairs later.
- Start hanging from a plumb line, not from a corner. Corners are rarely vertical.
- Begin in the least noticeable corner, often behind the door, because the pattern will not match where the last strip meets the first.
- Prepare walls properly. Fill holes, sand smooth, and apply a wallpaper primer or size so the paper slides into position and can be removed later.
- Check each roll for flaws before cutting.
- Use paste-the-wall papers if you are new to wallpapering. They are easier to handle than paste-the-paper types.
- Smooth from the centre outward to push out air bubbles.
Common Mistakes
Dividing area by roll coverage. This ignores unusable ends and pattern matching, and nearly always gives too few rolls.
Ignoring the pattern repeat. A large repeat can turn four strips per roll into three, increasing the order by a third.
Subtracting windows. The paper above and below a window still comes from full-length strips.
Mixing batches. A slightly different shade on one wall is obvious once it is up.
Not allowing trimming length. Ceilings and baseboards are not level. Each strip needs a couple of inches at both ends.
Skipping wall preparation. Paper shows every bump and will not stick to dusty or glossy surfaces.
Types of Pattern Match
A random or free match has no alignment between strips, and there is almost no waste. A straight match lines up horizontally, so every strip is cut at the same point in the pattern. A drop or half-drop match shifts each alternate strip by half the repeat, which looks more natural with large motifs and wastes more paper. The label states the match type and the repeat distance.
Wallpaper Materials
Non-woven papers are the most common now. They are strong, breathable and strip off in full sheets. Vinyl-coated papers are washable and suit kitchens and bathrooms. Traditional paper is delicate when wet and needs soaking time. Grasscloth and other natural textures have no pattern match but show every seam, so plan the strip positions carefully.
Paste and Tools
Check whether the paper is prepasted, paste-the-wall or paste-the-paper. One packet of paste typically hangs four to six rolls. You will also need a plumb line or level, a smoothing brush or plastic smoother, a sharp snap-off knife with spare blades, a seam roller and a clean sponge.
Papering a Feature Wall
A single papered wall is a common way to use a bold design without overwhelming a room. Measure the wall width in inches, divide by the roll width and round up to get the strips. Centre the pattern on the wall by starting with a strip at the middle and working outward in both directions, which keeps the design symmetrical at both corners. A 12 foot wall needs 8 strips of 20.5 inch paper. At three strips per roll, that is 3 rolls.
Ceilings, Slopes and Stairwells
On a sloped attic wall, measure the longest strip and use that as the height. Every strip is cut from full length even though most are shorter, so waste is high. Stairwells are estimated the same way, using the tallest wall height. These areas are the hardest to hang, and it is reasonable to add two spare rolls instead of one.