How many rolls of wallpaper do I need?

Total the wall area, add for trim and pattern matching, then divide by the usable area one roll gives and round up. A 12 by 9 foot wall is 108 square feet; at 25 usable square feet a roll, with a 15% pattern-and-trim allowance, you need about 5 rolls. This tool does that once you enter the wall and the roll coverage.

Why does a patterned paper need more rolls?

Every drop has to line up with the one beside it, so you cut off part of each length to bring the pattern back to the top — the bigger the repeat, the more you throw away. That is what the pattern-repeat allowance covers. A plain or random-match paper wastes almost nothing, so you can drop that allowance close to zero.

Should I count the doors and windows?

For a small opening, leave the wall whole — the trim allowance absorbs it and you keep a margin for mistakes. For a large window or a doorway, subtract that area from the wall you enter so you are not buying rolls to paper a hole. The tool covers exactly the area you give it.

Wallpaper calculator

The count spreads your wall area across rolls after two allowances you control. Pattern matching is unpredictable and papers differ in how they are measured, so order from one batch and buy a spare roll — a shortfall on the last wall means a visible seam of a different dye lot.

Enter the combined wall length and the height, the usable area a roll gives, and two allowances — trim for the top-and-bottom cuts, and a pattern-repeat margin for lining the drops up. The tool works out the area, applies both, divides by a roll and rounds up.

Worked example

A run of wall 12 ft long and 9 ft high is 108 square feet. Add 10% trim and 15% pattern repeat — 25% together — and you are hanging about 135 sq ft. At 25 usable square feet a roll that is 135 ÷ 25 = 5.4, so 6 rolls. A plain paper with no repeat would drop that toward 5.

The formula

rolls = (area × (1 + trim + repeat)) ÷ usable area per roll, rounded up

The wall area is length times height. Both allowances are added together and applied to it, because trim and pattern loss stack. Dividing by the roll's usable area — not the raw roll — gives the roll count, and rounding up turns it into what you buy.

Questions

How many rolls of wallpaper do I need?: Total the wall area, add for trim and pattern matching, then divide by the usable area one roll gives and round up. A 12 by 9 foot wall is 108 square feet; at 25 usable square feet a roll, with a 15% pattern-and-trim allowance, you need about 5 rolls. This tool does that once you enter the wall and the roll coverage.
Why does a patterned paper need more rolls?: Every drop has to line up with the one beside it, so you cut off part of each length to bring the pattern back to the top — the bigger the repeat, the more you throw away. That is what the pattern-repeat allowance covers. A plain or random-match paper wastes almost nothing, so you can drop that allowance close to zero.
Should I count the doors and windows?: For a small opening, leave the wall whole — the trim allowance absorbs it and you keep a margin for mistakes. For a large window or a doorway, subtract that area from the wall you enter so you are not buying rolls to paper a hole. The tool covers exactly the area you give it.

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