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Curtain fabric is calculated from gathered width, not window width: multiply the track by the fullness ratio, divide by the roll width and round up to whole widths. Each cut length is the finished drop plus about 30 cm for hem and heading.
Curtain fabric
gathered width = track x fullness; widths = ceil(gathered / roll width); length = widths x (drop + allowance)
2 to 2.5 times for pencil pleat, 2.5 for pinch pleat, and as little as 1.5 for eyelet headings on a plain fabric.
Each cut must start at the same point in the pattern, so add one repeat length per width. On a large repeat this adds substantially to the total.