The Wallpaper Calculator calculates how many rolls of wallpaper to buy using the strip (drop) method that decorators use.
It works out how many vertical strips cover the walls (total width ÷ roll width), how many full-height strips you can cut from one roll (roll length ÷ (wall height + pattern repeat), rounded down), and divides to get the number of rolls.
Wallpaper Calculator
How many rolls of wallpaper you need, using the strip method with roll width, roll length and pattern repeat.
Formula
- Strips needed: ⌈W ÷ roll width⌉
- Strips per roll: ⌊roll length ÷ (H + pattern repeat)⌋
- Rolls: ⌈strips needed ÷ strips per roll⌉
Where W = total width of the walls to cover and H = wall height.
How the Calculation Works
Step 1: Divide the total wall width by the roll width to find how many drops you need.
Step 2: Divide the roll length by the drop length (height plus one pattern repeat for matching) and round down — leftover pieces shorter than a full drop can’t be used.
Step 3: Divide drops needed by drops per roll and round up.
Variables Explained
| Input | Meaning |
|---|---|
| Width to cover | Sum of the widths of all walls being papered |
| Wall height | Floor (or baseboard) to ceiling (or crown) |
| Roll width, length | From the wallpaper label |
| Pattern repeat | Vertical distance before the pattern repeats (0 for random match) |
Example Calculation
Given: walls totaling 40 ft wide, 8 ft high, roll 20.5 in wide × 33 ft long, no repeat
Strips: 480 ÷ 20.5 = 23.4 → 24
Strips per roll: 33 ÷ 8 = 4.1 → 4
Result: 24 ÷ 4 = 6 rolls
With a 21 in pattern repeat
Each drop becomes 8 ft + 1.75 ft = 9.75 ft, so a roll gives only 3 strips: 24 ÷ 3 = 8 rolls.
Material Estimation Notes
- Roll sizes vary widely between brands and regions — always use the label dimensions.
- Buy all rolls from the same batch (lot number) so the color matches.
- Don’t subtract small openings; the offcuts rarely fit elsewhere. Large windows or doors can reduce the strip count.
Waste Factor Considerations
Pattern matching, trimming at the ceiling and baseboard, and corners all use extra. Many decorators buy a spare roll for mistakes and future repairs.
Frequently Asked Questions
How many rolls of wallpaper do I need?
Strips needed ÷ strips per roll, rounded up.
How does pattern repeat affect wallpaper?
Each strip must be longer to line up the pattern, so you get fewer strips per roll.
Should I subtract doors and windows?
Usually only large ones; offcuts from small openings are rarely reusable.
How do I measure for wallpaper?
Measure the width of each wall and add them, then measure the height to be covered.
What is a half-drop match?
A pattern that lines up halfway down the next strip; enter the pattern repeat from the label.