Wallpaper calculator: how many rolls you need, with pattern repeat

Wallpaper is counted in drops: total wall length ÷ roll width gives the number of drops, and roll length ÷ drop length gives the drops per roll. With a 2.4 m wall, a 10.05 m roll gives four drops.

Why count drops, not square metres

The standard Euro roll, as the German maker A.S. Création describes it, is 10.05 m long and 0.53 m wide: 5.33 m² of paper. Dividing the wall area by 5.33 looks sensible, but a roll is cut into drops the height of the wall, and the piece left at the end is often too short for one more drop.

Example: a 4 × 3 m bedroom has 14 m of wall. With a 2.4 m ceiling you need 14 ÷ 0.53 = 26.4, so 27 drops of 2.45 m including the allowance. Each roll gives 4 drops, so 7 rolls, with only 0.25 m wasted per roll. Raise the ceiling to 2.5 m and each drop becomes 2.55 m: a roll now gives 3 drops and leaves 2.40 m of waste, so the same room needs 9 rolls. Working by area would still say 7.

Drops per 10.05 m roll by wall height and pattern repeat

Each cell gives the number of full drops cut from one roll and, in brackets, the length of each drop including a 5 cm trimming allowance. Example: with a 2.50 m wall, a paper with no repeat is cut into 2.55 m drops and one roll gives 3 of them.

How the pattern repeat changes the count

A patterned paper has to line up from one drop to the next, so each drop is a whole number of repeats: the wall height plus the allowance, rounded up to the next repeat. The wallpaper maker meinewand works through a 2.65 m wall with a 72 cm repeat: 3.68 repeats, rounded up to 4, giving drops of 2.88 m and 3 drops from a 10.05 m roll. A 5 m wide wall then needs 10 drops and 4 rolls.

In the 2.4 m bedroom, a 53 cm repeat lengthens each drop from 2.45 m to 2.65 m. A roll then gives 3 drops instead of 4, and the order goes from 7 rolls to 9. Enter the repeat printed on the label, whether it is a straight match or a half-drop match.

Trimming allowance and spare paper

Each drop is cut longer than the wall so it can be trimmed neatly at the ceiling and the skirting. A.S. Création suggests adding about 5 cm to the room height to avoid a tight cut, which is the calculator's starting allowance; you can change it in the settings.

Graham & Brown advises allowing an extra 10% for waste and points out that the right amount depends on the match type and the size of the repeat; B&Q's calculator also recommends at least 10% extra. Buy every roll from the same batch, and tick the spare roll box if you want one kept back for repairs.

Doors and windows

Above a door and below a window you still need short pieces, so an opening rarely saves a whole drop. Graham & Brown recommends measuring the full walls and not taking doors and windows off, treating the small surplus as protection against mistakes, and A.S. Création suggests covering them with spare rolls. The calculator follows that advice and deducts nothing for openings.

Mistakes that cost a roll

• Working by area: in the 2.5 m bedroom, 7 rolls instead of 9.
• Ignoring the repeat: at 2.4 m, a 53 cm repeat turns 4 drops per roll into 3.
• Measuring the height in the middle of the wall when the ceiling is not level: use the tallest point.
• Assuming every roll is 10.05 × 0.53 m: check the width and length on the label and change them in the settings.

To prepare the job, the perimeter of the room gives the length of wall, paint for the ceiling is worked out per square metre, and the mitre angle helps with coving and skirting.