Wallpaper should be calculated in full drops, not simply by dividing wall area by roll area. The Wallpaper calculator uses wall length, height, roll size, trimming allowance and pattern repeat.
For 12 m of wall and a 0.53 m roll, at least 23 drops are needed before any extra allowance. With a 2.50 m wall and 10 cm trimming allowance, each drop needs at least 2.60 m.
Pattern repeat changes usable length
With a 64 cm repeat, 2.60 m must be rounded up to a multiple of 0.64. Five repeats give 3.20 m per drop. A 10.05 m roll then provides only three complete drops.
This is why the theoretical square metres printed for a roll can be misleading: offcuts cannot always be rearranged while preserving a full-height matching pattern.
Doors, windows and offcuts
Unlike paint, openings do not necessarily remove a full wallpaper drop. Pieces above a door or below a window may be reusable, depending on the pattern. A conservative drop-based estimate is therefore often safer than automatically subtracting every opening.
Check the manufacturer’s instructions for straight match, offset match or other special patterns. Also check batch numbers: the same design from different batches can show a slight colour variation.
For a painted finish use the Paint calculator. For a new wall substrate use the Drywall calculator.
Measure total wall length and height, enter the exact roll dimensions and repeat, then round to complete rolls. Decide separately whether you want an additional maintenance roll from the same batch.
