Wallpaper calculator
How many rolls of wallpaper to buy for a room, worked out from the roll's own width, length and pattern repeat.
How the number is worked out
- Measure the walls. Each wall's width, and the height from the skirting to the ceiling.
- Find the drop length. A drop is one full-height strip. Add 10 cm to the height for trimming. With a straight or half-drop match, round that up to whole pattern repeats, and add half a repeat for a half-drop.
- Count the drops from one roll. The roll's length divided by the drop length, rounded down. A part-drop left on the roll is waste.
- Count the drops for the room. Each wall's width divided by the roll's width, rounded up, then all the walls added together.
- Count the rolls. All the drops divided by the drops from one roll, rounded up.
Doors and windows are not taken off. The pieces above and below them still come from full drops, and every corner wastes a strip.
A worked example
A room 4.2 m by 3.6 m with walls 2.4 m high, papered with rolls 53 cm wide and 10.05 m long. These are example figures, not a product.
| Working | Plain paper | 53 cm straight-match repeat |
|---|---|---|
| Drops for the four walls | 30 | 30 |
| Drop length | 2.5 m | 2.65 m |
| Drops from one roll | 4 | 3 |
| Rolls to buy | 8 | 10 |
| Spare drops | 2 | 0 |
The repeat turns a 2.5 m drop into 2.65 m. Only 3 fit on a roll instead of 4, so the same room needs 2 more rolls. Copy the width, length, repeat and match from your own roll's label: they change the answer.
Mistakes that cost a roll
- Dividing the wall area by the area of one roll. It ignores the paper lost to matching a pattern. In the example it says 8 rolls for the paper with the repeat, which needs 10.
- Leaving out the pattern repeat. In the example it is worth 2 rolls.
- Taking the doors and windows off. The pieces above and below them are cut from full drops so the pattern lines up, and each corner wastes a strip.
- Buying rolls from different batches. The colour can differ from one batch to the next. The label shows the batch number.
- Buying with no spare drop. With 0 spare drops, one mis-cut leaves you a roll short. The planner warns you when that happens.
Questions
What is a pattern repeat?
How far up the roll the pattern runs before it starts again. It is printed on the roll's label, in centimetres. A plain or textured paper has none to line up.
What are straight, half-drop and free matches?
With a straight match the pattern lines up straight across from drop to drop. With a half-drop match every other drop is offset by half a repeat, so each drop needs half a repeat more paper. A free match has no pattern to line up.
Do I take off the doors and windows?
No. The pieces above and below them still come from full drops, and every corner wastes a strip. Counting whole drops for every wall errs towards a spare drop rather than a wall left short.
Which roll size does it start with?
A common UK roll, 53 cm wide and 10.05 m long, with no pattern repeat. It is a labelled example, not a product. Change it to the figures on your roll's label.
Does it count paste?
Yes, if you enter how many rolls one packet hangs. The packet says. Without that figure the line tells you to check the label, because some papers are ready-pasted.