Whole rolls, one dye lot, no mid-wall surprises

Rolls needed are wall area ÷ one roll's coverage, plus wastage, rounded up to whole rolls: 10 m² at 5 m² per roll with 10% waste is ceil(10 ÷ 5 × 1.1) = 3 rolls. Fractions round up because rolls sell whole — and a large-repeat pattern eats extra length aligning across drops, which is what the waste margin is really for.

Subtract large windows and doors from the wall area (keeping overlap for matching), enter the roll's coverage from its label, and set waste by the pattern repeat — 10% plain, more for big repeats. Then buy every roll together: dye lots differ between batches, so a later top-up may stripe against the first hanging.

It does not lay out drops, match pattern repeats, or price paste and labour — a roll count from one batch, with cutting left to the hanger's judgement.

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