Draper

A curtain is gathered, so it needs far more fabric than the window is wide, cut off a roll in whole widths. Draper works out the metres to order, the number of widths, the cut length and the waste.

The window

Measure the track or pole end to end, and the drop from the top of the heading to where you want the hem, with the track already up.

The heading

The fabric

A pattern repeat makes each drop round up to a whole repeat so the pattern lines up across the joins. Leave it at 0 for a plain fabric.

Why a curtain needs so much fabric

You don't buy curtain fabric by the window; you buy a length off a roll that comes in a set width, usually 137 cm, and a curtain is gathered so it hangs in folds. The heading sets how full that gather is: pencil pleat and eyelet take about twice the track width of flat fabric, pinch pleat a little more. Draper multiplies the track by that fullness, adds the returns to the wall and the centre overlap, then cuts the flat width out of the roll in whole widths joined side by side. Each drop is cut to the finished length plus a turn at the top and a hem at the bottom, rounded up to a whole pattern repeat if the fabric is patterned, because every drop has to start on the same point so the pattern lines up across the joins. These are planning figures: measure the drop with the track up, check the fabric width with the shop, and buy it all from one roll so the colour matches.