How the wallpaper calculator works
Wallpaper is hung in vertical strips called drops. The calculator counts how many roll-widths fit across the wall, works out the cut length of each drop (height plus trim, rounded up to the pattern repeat), and how many complete drops each roll yields.
Dividing drops by drops per roll and rounding up gives the rolls to buy. This is more reliable than dividing wall area by roll area, which ignores offcuts at the top of each roll.
Formula and assumptions
- repeat
- vertical pattern repeat from the label (0 for free match)
- trim
- extra length for top and bottom trimming
Assumptions and limits
- Straight or free match. Half-drop and mural designs need product-specific planning.
- Doors and windows are not subtracted; they rarely save a full drop.
Worked example
A 12 ft wide, 8 ft high wall, 20.5 in wide × 33 ft rolls (example), no repeat, 4 in trim.
- 12 ft = 144 in; 144 ÷ 20.5 = 7.02, so 8 drops.
- Cut length = 96 + 4 = 100 in (8.33 ft).
- 33 ÷ 8.33 = 3.96, so 3 drops per roll.
- 8 ÷ 3 = 2.67; round up to 3 rolls.
These are the calculator’s default values, so the live result above matches this example until you change an input.
How to measure correctly
- Measure the widest point of each wall and add the walls you will paper.
- Measure height at the tallest point.
- Read the roll width, roll length, and repeat from the label; roll sizes vary by brand and region.
Wallpaper Calculator FAQ
How many rolls of wallpaper do I need?
Count drops (wall width ÷ roll width, rounded up), find complete drops per roll (roll length ÷ cut length, rounded down), then divide and round up.
How does pattern repeat affect wallpaper?
Each drop must start at the same point in the pattern, so the cut length rounds up to a multiple of the repeat. Large repeats can cut the drops per roll and raise the roll count.
Should I subtract windows and doors?
Usually not. A window removes only part of a drop, and the pieces above and below still come from full lengths.
What is a double roll?
In the US, wallpaper is often priced per single roll but packaged in double rolls. Enter the physical roll length you will receive.
How much extra wallpaper should I buy?
The spare drops figure shows what is left over. Many people keep at least one spare roll from the same batch for repairs, since batches can vary in color.
Does this work for peel-and-stick wallpaper?
Yes. Enter the panel width and length as the roll size.