Dividing the wall area by the area of a roll gives the wrong answer for wallpaper. Paper is hung in drops from ceiling to skirting, and the leftover at the end of each roll is usually too short for another drop.
Drops per roll
A standard roll is 10.05 m long and 53 cm wide. Graham & Brown and Bunnings both list that size. For a 2.4 m wall with 10 cm for trimming, each drop is 2.5 m, and a roll gives four drops with 5 cm over.
A pattern repeat makes each drop longer, because the next drop has to start where the pattern matches. With a 64 cm repeat, 2.5 m becomes four repeats, 2.56 m, and a roll gives only three drops.
| Walls round the room | No repeat | 26 cm | 53 cm | 64 cm |
|---|---|---|---|---|
| 12 m (3 × 3 m room) | 6 | 8 | 8 | 8 |
| 14 m (3 × 4 m room) | 7 | 9 | 9 | 9 |
| 18 m (4 × 5 m room) | 9 | 12 | 12 | 12 |
Widths
The number of drops is the width of the walls divided by the roll width, rounded up. 14 m of wall at 53 cm is 27 drops. At four drops a roll that is 7 rolls; at three a roll it is 9.
Farrow & Ball's guidance gives the same pattern: about four drops a roll for a stripe or free match, three for a small repeat and two for a large one.
Doors and windows
The calculator does not take off doors and windows. The short pieces above and below them usually come from offcuts, and the extra covers a mistake or a torn drop. Higher ceilings change the count quickly: at 2.7 m, the 3 × 4 m room needs 9 rolls even without a repeat.
Batches
Check that every roll has the same batch number; colour can vary between print runs. Buy one spare from the same batch if the room is awkward or the pattern is large.
Figures are estimates for a shopping list. Check the pack or datasheet before you buy.