What this calculator does
Find out how many rolls of wallpaper to buy for your room, so you don't run short halfway along a wall. Wallpaper goes up in strips that run from ceiling to floor, each cut from a roll. So the number of rolls depends less on the wall's area. It depends more on how many full-height strips you need, and how many fit in one roll. Patterned paper wastes extra length on every strip. That's because each strip has to start at the same point in the design as the one beside it. This calculator counts strip by strip, rather than dividing areas, which tends to come up short.
Enter the total width of the walls, their height and the width of any doors. Then add the roll's width and length from the label, plus the pattern repeat. The calculator rounds each strip up to a whole number of repeats. It counts how many complete strips each roll gives you. Then it tells you how many rolls to buy.
Where it's used
Why this math matters outside the classroom:
- Strip count. A 12 ft wall with 21 in wide rolls needs 144 ÷ 21 ≈ 6.9, so 7 strips.
- Pattern repeat. On an 8 ft wall with a 4 in trim allowance and a 21 in repeat, each strip uses 105 in of paper, five full repeats.
- Strips per roll. A 33 ft roll is 396 in long, so it gives three full 105 in strips.
- Rolls to buy. Seven strips at three per roll means 7 ÷ 3 ≈ 2.33, so the decorator buys 3 rolls.
- Accent walls. Homeowners papering a single accent wall work out the roll count for that wall alone to keep the cost down.
How to use it
- Choose US units or metric units.
- Enter the combined width of all the walls you are papering and their height, plus the width of doors or other full-height openings.
- Enter the roll width, roll length and pattern repeat printed on the label. Add a trimming allowance (a little extra length to trim off).
- Read the number of rolls. Buy them all from the same batch, so the color matches.
What the inputs mean
- Total width of walls to cover
- Add up the widths of every wall. For a whole room, that's the distance all the way around it.
- Width of doors and full-height openings
- Only full-height openings such as doors and wide archways are taken off. Windows are left in on purpose. The short pieces above and below a window usually come from strips you'd cut anyway.
- Roll length
- Rolls come in different sizes in different countries. So always use the figures on the label of the paper you're buying.
- Pattern repeat
- How far down the paper you go before the design starts over. It's printed on the label. Enter 0 for plain paper or a random match (paper with no pattern to line up). For a drop match, use the repeat as printed; the math is the same.
- Trimming allowance per strip
- Extra length so you can trim each strip neatly at the ceiling and the baseboard. About 2 inches (5 cm) at each end is common.
Formula and method
strips = ceil((wall width − openings) ÷ roll width) strip length = wall height + trimming allowance cut length = ceil(strip length ÷ repeat) × repeat (or strip length if there is no repeat) strips per roll = floor(roll length ÷ cut length) rolls = ceil(strips ÷ strips per roll)
In the formulas, "ceil" means round up to the next whole number, and "floor" means round down. A "drop" is one full-height strip. The cut length is that strip after it's lengthened to match the pattern. Strips are rounded up, because a part-width strip still needs its own full drop. Strips per roll are rounded down, because a leftover piece shorter than a full drop can't make one. The final count is rounded up to whole rolls.
Widths are changed to inches (1 ft = 12 in) or centimeters (1 m = 100 cm). That way they can be compared directly with the roll width and the repeat.
Worked example
A 12 ft × 12 ft room (48 ft of wall) has 8 ft walls and doors totaling 6 ft wide. The paper comes in rolls 20.5 in wide and 33 ft long, with an 18 in pattern repeat. Allow 4 in for trimming.
- Width to cover: (48 − 6) × 12 = 504 in.
- Strips: 504 ÷ 20.5 = 24.59, rounded up to 25 strips.
- Strip length: 8 × 12 + 4 = 100 in, which needs 6 repeats of 18 in, so cut 108 in.
- Strips per roll: 33 × 12 = 396 in ÷ 108 = 3.67, rounded down to 3.
- Rolls: 25 ÷ 3 = 8.33, rounded up to 9 rolls.
Result: Buy 9 rolls. Each roll yields three 108 in strips and leaves a 72 in offcut.
Understanding the result
The offcut (the leftover piece) on each roll shows how much the pattern repeat is costing you. A large offcut may come in handy for the short pieces above doors and around windows.
Buy all rolls with the same batch or lot number, because colors can vary slightly between print runs. Many decorators buy one extra roll for mistakes and future repairs.
Assumptions and limitations
- All walls have the same height.
- Every strip is cut to the full wall height plus the trimming allowance.
- Offcuts are not joined to make full strips.
- Sloping ceilings, stairwells and walls of different heights should be calculated separately and added together.
- Large windows and features such as fireplaces may save some paper that this count does not credit.
- Hanging mistakes and damaged strips aren't included, so think about getting a spare roll.
Frequently asked questions
What is a pattern repeat?
It's how far down the paper you go before the design starts over. Each strip has to be cut so its pattern lines up with the strip beside it. That means rounding the strip length up to a whole number of repeats. Large repeats can waste a good part of each roll.
Why not just divide the wall area by the roll area?
Because paper goes up in full-height strips, not by the square foot. In theory, a roll might cover a certain area. But once each strip is cut to length and matched, it may only give three usable strips. So the area method usually comes up short.
Should I subtract windows?
Usually not. The pieces above and below a window come from strips that are cut to full length anyway. So a window rarely saves a whole strip. Only doors and openings that run nearly floor to ceiling are worth taking off.
What is a drop match?
In a drop (or half-drop) match, the design on each strip sits a little higher or lower than on the strip beside it. Each strip is still cut to a whole number of repeats from where the last one started. So the same math applies. You may lose a little more paper at the top of every other strip.
How this calculator is checked
Method: Strip-per-roll method used in decorating practice: strips = ceil(width ÷ roll width), strips per roll = floor(roll length ÷ matched drop). The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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