Pattern Repeat for Curtains, Explained

A patterned fabric has to match across every width, so each drop is cut to a whole number of pattern repeats. A half-drop repeat, where the pattern steps down on alternate widths, needs one extra repeat added to the order. This is the part most calculators get wrong.

What a pattern repeat is

A patterned fabric repeats its design down the roll at a fixed interval, the pattern repeat. To make curtains, you join several widths of fabric side by side, and the design has to line up across every join or the eye catches the break at once. So instead of cutting each width to the exact drop, you cut it to the next whole number of repeats above the drop. Every width then starts at the same point in the pattern and matches its neighbour.

That rounding is why a patterned fabric always uses more than a plain one. A 230 cm cut on a plain fabric stays 230 cm. On a fabric with a 64 cm repeat, you round up to four repeats, which is 256 cm per width. Over four widths that is an extra metre of cloth, built in before you account for the kind of repeat.

Straight repeat versus half-drop

There are two kinds of repeat, and they are not the same to calculate:

• Straight repeat: the pattern lines up directly across the width. The motif at a given height on one width sits at the same height on the next. You just round each width up to a whole repeat.
• Half-drop repeat: the pattern steps down by half a repeat on every other width, so the design runs on a diagonal. Lovely to look at, trickier to cut. To bring the alternate widths back into match, you add one whole extra repeat to the order.

The half-drop rule, done right

This is the part most calculators get wrong, and it is where fabric gets wasted. For a half-drop repeat you add one whole pattern repeat to the total order, once, not one per width. Half of that extra repeat positions the pattern and half offsets the alternate drops when the cutter steps down to start the even-numbered widths (sew-helpful.com). Add a repeat per width and you over-order badly; add nothing and your widths will not match.

The curtain fabric calculator handles both cases. Choose straight repeat and it rounds each width up to a whole repeat. Choose half-drop and it does that and adds the single extra repeat to the job. The cut list it prints shows the exact length for every drop plus the half-drop allowance on its own line, so the workroom cuts with no guesswork.

Why getting it wrong is expensive

Pattern repeats are large on the kind of fabric people choose for curtains, often 30 to 90 cm. On a tall drop, one extra repeat per width that you did not need is roughly a width of waste. On a large pair in a mid-priced fabric, that is commonly $100 to $400 of cloth bought and not used, or worse, a shortfall found halfway through cutting when the dye lot is gone. A correct repeat calculation is the single biggest saving this tool makes.

Ready to order? Run your numbers through the calculator. New to measuring? Start with how to measure for curtains and the fullness and pleat guide.