Wallpaper is one of the easiest materials to under-order — and one of the hardest to fix if you do. Unlike paint, you cannot mix a slightly larger batch. If you run short and re-order, the new rolls may come from a different dye lot and the colour will not match exactly. Getting the count right before you buy is the only safe approach.
This guide walks through the complete calculation — from measuring the room to accounting for pattern repeat — so you can order with confidence.
What You Need Before You Start
- Room perimeter — total width of all walls you are papering
- Ceiling height — floor to ceiling, including any cornice or coving you will paper over
- Roll dimensions — standard UK/EU rolls are 10 m long × 0.52 m wide; US double rolls are typically 13.7 m × 0.68 m
- Pattern repeat — printed on the label; 0 means no repeat (plain or texture)
- Match type — straight match or drop match (also on the label)
The Basic Formula
Without a pattern repeat, the calculation is straightforward:
- Calculate the drop length — ceiling height + 100 mm trimming allowance top and bottom
- Calculate strips per roll — roll length ÷ drop length (round down)
- Calculate total strips needed — room perimeter ÷ roll width (round up)
- Calculate rolls needed — total strips ÷ strips per roll (round up)
Example: Room perimeter 14 m, ceiling height 2.4 m, standard roll (10 m × 0.52 m), no pattern:
- Drop length: 2.4 + 0.2 = 2.6 m
- Strips per roll: ⌊10 ÷ 2.6⌋ = 3 strips
- Total strips: ⌈14 ÷ 0.52⌉ = 27 strips
- Rolls needed: ⌈27 ÷ 3⌉ = 9 rolls
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Open Wallpaper CalculatorPattern Repeat — the Part People Get Wrong
When your wallpaper has a pattern, every strip must start at the same point in the repeat so the pattern lines up across the wall. This means you will waste some paper at the top or bottom of each strip to find the matching start point.
The adjusted drop length with pattern repeat is:
Adjusted drop = ceiling height + trimming allowance + pattern repeat
Example: Same room as above, but with a 64 cm pattern repeat:
- Adjusted drop: 2.4 + 0.2 + 0.64 = 3.24 m
- Strips per roll: ⌊10 ÷ 3.24⌋ = 3 strips
- Total strips: 27 (unchanged)
- Rolls needed: ⌈27 ÷ 3⌉ = 9 rolls
In this case the roll count did not change — but with a larger repeat or lower ceiling, it can easily add one or two rolls.
| Pattern repeat | Extra waste per strip | Impact on roll count |
|---|---|---|
| 0 (plain / texture) | None | Baseline |
| Up to 30 cm | Small | Rarely adds a roll |
| 30–64 cm | Moderate | Often adds 1 roll per room |
| 64 cm+ | Significant | Can add 2+ rolls per room |
Straight Match vs. Drop Match
The match type affects how much waste you get from each roll.
Straight match
Every strip starts at the same point in the repeat. The pattern runs horizontally across the wall. Waste per strip = pattern repeat ÷ 2 on average.
Drop match (half drop)
Alternate strips are offset by half the pattern repeat. This means odd strips start at one point, even strips start half a repeat lower. You effectively need two sequences of cuts, which increases waste.
For a half-drop match, use:
Adjusted drop = ceiling height + trimming allowance + (pattern repeat × 1.5)
Deducting Doors and Windows
You can subtract door and window openings from the total perimeter — but be cautious. The strips beside openings often have awkward cuts and the off-cuts are rarely long enough to reuse elsewhere.
A conservative approach: subtract only openings wider than the roll width, and only deduct half the calculated saving. This gives you a small buffer without over-ordering significantly.
As a rough guide:
- Standard door (0.9 m wide): deduct 1 strip
- Standard window (1.2 m wide): deduct 1 strip
- Large window or patio door (1.8 m+): deduct 2 strips
From Metres to Rolls
Once you have the total strips needed, divide by strips per roll and round up. Always add at least one extra roll as a buffer — both for mistakes during hanging and for future repairs.
Rolls to buy = ⌈total strips ÷ strips per roll⌉ + 1 buffer roll
5 Common Mistakes
1. Forgetting the pattern repeat entirely
A large pattern repeat can add 10–20% to your roll count. Many people calculate based on plain wallpaper coverage figures and run short once they start cutting.
2. Using perimeter without subtracting anything
The opposite error — not deducting doors and windows at all leads to over-ordering. One or two rolls of buffer is sensible; five is wasteful.
3. Confusing roll length with usable length
A 10 m roll does not give you 10 m of usable drops. After trimming and pattern matching, 3 strips per roll is common on a standard ceiling height with a moderate repeat.
4. Different roll widths for the same room
If you buy a mix of roll widths (say 0.52 m and 0.53 m), the strips will not align. Always stick to the same product and roll width throughout a room.
5. Not checking the batch number at the shop
If the shop pulls rolls from two different boxes, check that the batch numbers match before you leave. Mixing batches is how colour mismatches happen.
Quick Reference
| Step | Formula |
|---|---|
| Drop length (no repeat) | ceiling height + 0.2 m |
| Drop length (straight match) | ceiling height + 0.2 m + repeat |
| Drop length (half-drop match) | ceiling height + 0.2 m + (repeat × 1.5) |
| Strips per roll | ⌊roll length ÷ drop length⌋ |
| Total strips | ⌈perimeter ÷ roll width⌉ |
| Rolls to buy | ⌈total strips ÷ strips per roll⌉ + 1 |
Ready to get your exact number? Use our wallpaper calculator — enter your room dimensions, roll size and pattern repeat for an instant roll count.