Count drops, not area
Wallpaper is hung in full-height strips called drops, and a roll gives a whole number of them. Working in square meters hides that, which is why area-based answers come out short.
- Measure the perimeter of the room: add up the width of every wall.
- Divide by the roll width to get the number of drops.
- Work out how many drops come out of one roll: roll length ÷ drop length.
- Divide the drops you need by the drops per roll, and round up.
A worked example
A room 4 m by 3 m with a 2.4 m ceiling, papered with a standard European roll of 0.53 m by 10 m.
- Perimeter: 4 + 3 + 4 + 3 = 14 m.
- Drops: 14 ÷ 0.53 = 26.4, so 27 drops.
- Plain paper: 10 ÷ 2.4 = 4.1, so 4 drops a roll, and 27 ÷ 4 = 7 rolls.
What the pattern repeat does
With a pattern, every drop has to start at the same point in the design, so each drop is the wall height rounded up to a whole repeat.
- A 64 cm repeat on a 2.4 m wall: 2.4 ÷ 0.64 = 3.75, rounded up to 4 repeats, so each drop is 2.56 m.
- 10 ÷ 2.56 = 3.9, so only 3 drops a roll.
- 27 ÷ 3 = 9 rolls, two more than the same room in a plain paper.
A straight match lines up across the seam; an offset or half-drop match stagger the design, which uses a little less because the off-cut from one drop starts the next. The roll label says which it is.
Doors, windows and chimney breasts
Subtract only large openings: a patio door, or a run of windows. Leave small windows in the total, because the paper above and below them still comes off a full drop, and you need the off-cuts anyway. A chimney breast adds drops rather than removing them, since its sides need their own short pieces.
Buy it all at once
Rolls are printed in batches, and the color varies between them enough to see on a wall. Check that every roll carries the same batch number, and buy a spare: running one roll short in the same batch six weeks later is usually impossible.
Tools
The Wallpaper Calculator counts the drops and rolls for you, including the pattern repeat and the openings you leave out. The Paint Calculator does the same for the walls you are painting instead.