Wallpaper Calculator
Rolls for a room, with the pattern repeat accounted for, which is the thing that catches people out.
In short
Divide the wall height plus the pattern repeat into the roll length to get usable drops per roll, then divide the room perimeter by the roll width to get the drops needed. Pattern repeat is what makes two identically sized rooms need different amounts of paper.
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The calculation
- Drops needed. Room perimeter divided by roll width, rounded up. Deduct a little for large doors and windows.
- Length per drop. Wall height plus the pattern repeat allowance, plus about 10 cm for trimming top and bottom.
- Usable drops per roll. Roll length divided by length per drop, rounded down. A partial drop is waste.
- Rolls. Drops needed divided by drops per roll, rounded up.
The rounding down in step three is where the pattern repeat does its damage, and it is why the answer is not a smooth function of the numbers.
Why repeat matters more than area
Two rooms of identical size can need noticeably different amounts of paper purely because of the pattern.
A standard 10.05 m roll against a 2.4 m wall with plain paper gives four usable drops, with 0.45 m left over. Add a 64 cm repeat and each drop needs up to 3.04 m, so the same roll yields three drops. That is a 33% increase in rolls for the same room.
Which is why the repeat figure on the label is worth reading before you fall in love with a pattern. A large repeat on a tall wall can add meaningfully to the cost.
The three match types
| Type | How it aligns | Waste |
|---|---|---|
| Free match | No alignment needed | Minimal |
| Straight match | Same height on every drop | Up to one repeat per drop |
| Offset or drop match | Alternate drops staggered by half a repeat | Most, but often looks better |
Free match papers are usually textures, stripes or random designs. They are considerably more forgiving for a first attempt and cheaper to hang because so little is wasted.
Doors and windows
Do not simply subtract their area. A window in the middle of a wall still needs paper above and below it, and the offcuts rarely combine into a usable full drop.
A reasonable rule, used here, is to credit roughly half a drop for a standard door and a quarter for a large window. Small windows are best ignored entirely. Under-ordering is far more expensive than over-ordering, because a second batch may not match.
Batch numbers matter more than with paint
Wallpaper is printed in batches and shade varies between them, sometimes obviously. Adjacent drops from different batches show a visible line down the wall in daylight.
- Buy every roll at once.
- Check the batch numbers on the labels match before you leave the shop.
- Buy one spare roll from the same batch.
- If you must mix batches, use the odd ones on a separate wall rather than alongside.
Practical points
- Start from a corner near the door, so the inevitable mismatch where the pattern meets itself ends up in the least visible place.
- Hang the first drop against a plumb line, not the corner. Walls are rarely straight and the error compounds across the room.
- Cut all drops for a wall before pasting, checking the pattern lines up as you go.
- Leave 5 cm spare at each end for trimming.
- Ceilings are rarely level. Check before assuming a drop can be cut square.
Frequently asked questions
How many rolls of wallpaper do I need?
Divide the roll length by the drop height plus the pattern repeat to get usable drops per roll, then divide the room perimeter by the roll width to get how many drops you need. Divide one by the other and round up.
Why does pattern repeat matter so much?
Because each drop has to start at the right point in the pattern, so you waste up to one repeat per drop. A 64 cm repeat on a 2.4 m wall can cut a standard roll from four usable drops to three, which is a 25% increase in rolls for the same room.
What is a straight match and an offset match?
A straight match lines up at the same height on every drop. An offset or drop match staggers alternate drops by half a repeat, which wastes more paper but usually looks better on large patterns. Free match paper, with no alignment at all, wastes almost nothing.
Should I subtract doors and windows?
Only large ones. A standard door is worth deducting; a small window usually is not, because the offcuts above and below rarely make a full drop. The tool deducts partial credit rather than the full area, which reflects how the paper actually gets used.
Do I need rolls from the same batch?
Yes, and this matters more than with paint. Batch numbers are printed on the label and shade varies noticeably between them. Buy all your rolls at once, check the batch numbers match, and buy one spare.