Why rolls are counted in drops
A roll is cut into drops, one per strip of wall, and each drop has to be the wall height plus the pattern repeat so the pattern lines up across the joins.
Drops from one roll is the roll length divided by that cut length, rounded down. A 10 m roll with 2.4 m walls gives 4 drops; add a 0.32 m repeat and the cut length becomes 2.72 m, which gives only 3.
Drops needed is the wall perimeter divided by the roll width, rounded up. Every drop is a full height, so a door or window only saves a drop if it removes a whole width of wall.
Worked example
A room with a 12 m perimeter and 2.4 m walls, papered with 0.53 m wide rolls and no repeat, needs 23 drops. At 4 drops per roll that is 6 rolls.
The same room with a 0.32 m repeat needs 8 rolls, because each roll yields 3 drops instead of 4. That is a third more paper for the same wall.
Openings and matching
Doors and windows are entered as an area, which is converted back to a length of wall. That is the honest way to do it: a window 1.2 m wide in a 2.4 m wall removes half a drop, and the half drop cannot be used elsewhere.
Pattern matching also wastes the end of each roll. The last drop on a roll is often too short to use, which is why the drop count rounds down rather than up.
Buy one extra roll for a feature wall or for future repairs. A different dye lot will not match, and the same batch is rarely available later.
Limits of this calculator
It assumes walls of one height and a repeating pattern with a single repeat distance. A stairwell, a sloped ceiling or a mural panel needs each wall calculated separately.
It does not account for pattern matching across a corner, which can waste most of a drop, or for a paper with a half-drop match.
It does not include adhesive, lining paper or the cost. Those are separate quantities.
For a painted finish instead, use the paint calculator.
Inputs for the wallpaper calculator
Room perimeter
Total length of the walls to be papered, measured at skirting level.
Wall height
Floor to ceiling height, or to the picture rail if the paper stops there.
Doors and windows
Total area to leave out. Enter zero to paper around them.
Roll width
Width of one roll, 0.53 m for a standard roll.
Roll length
Length of one roll, 10 m for a standard roll.
Pattern repeat
Distance before the pattern repeats. Enter zero for a plain paper.
CALCULATOR QUESTIONS
Wallpaper calculator questions
How many rolls for a standard room?
A 12 m perimeter with 2.4 m walls takes about 6 rolls plain, and 8 with a 0.32 m repeat.
Do I subtract doors and windows?
Only the wall length they occupy. A window rarely saves a whole drop, so the saving is small.
Why does a pattern need more paper?
Each drop must be cut to the height plus the repeat, so fewer drops come from each roll.
Should I buy an extra roll?
Yes, if you can. Dye lots vary, and the same batch is often gone by the time you need a repair.