The repeat you did not budget for
Ask anyone what a pattern repeat costs and they will tell you about the vertical one. It is the visible tax: a 24 in repeat on a 26 in cut means 48 in of cloth, and everyone who has bought drapery fabric has had that conversation. The horizontal repeat rarely comes up at all, and it behaves completely differently — which is what makes it the one that ruins an order.
Here is why. When two widths are joined side by side, the design has to run across the seam without a jump. Both widths come off the same bolt at the same phase, so the pattern only continues automatically if the horizontal repeat divides evenly into the width you are left with after the selvage and the seam allowances. When it does not, the cutter trims each width back to the last whole repeat. That trim costs nothing per drop — the drop is the same length either way — and then it costs you a whole extra width once the arithmetic is done.
The two therefore have quite different shapes. Run this page over a few thousand combinations of panel size, goods width and repeat and the vertical rounding charges you something on about ninety-six per cent of them, averaging around a sixth of the order. The horizontal one charges you nothing at all on about ninety-two per cent — and then, on a small minority, adds forty per cent or more in a single step. It is not the bigger cost on average. It is the one that is invisible until it is enormous, and it is invisible because it does not show up anywhere in the yardage per drop.
What the defaults show
The form starts on a 54 in goods with 1 in of selvage off and a half inch seam allowance on each side, which leaves 52 in of width to match on. Against a 13.5 in horizontal repeat that is three whole repeats, or 40.5 in, and 11.5 in comes off every width. Covering 96 in then takes three widths instead of the two a plain cloth would need. Per panel, per drop, nothing changed. In total, the job grew by half.
The vertical side is doing its own work at the same time. An 84 in panel with 10 in of header and hem is a 94 in cut, which rounds up to six 18 in repeats — 108 in, with 14 in of offcut on every drop. And because the default is a half drop, another 9 in comes off the roll between one drop and the next so the alternate widths sit half a repeat lower, which across six drops is 45 in.
Put together, the pair of panels takes 20-7/8 yd. The same pair on a plain cloth takes 11-3/8 yd — 83 per cent more fabric. The side match is the larger half of that: turn the vertical repeat off and leave the 13.5 in horizontal one, and the job is still 17 yd. Turn the horizontal one off and leave the vertical, and it is 13-7/8. On these particular numbers the one nobody budgets for costs more than the one everybody does, which the section above says is the unusual case rather than the normal one — and that is exactly why it is worth a page.
Bigger repeats are not always worse
This is the claim the page refuses to make, and it prints the counterexample instead. At an 18 in repeat the 94 in cut wastes 14 in. Push the repeat to 18.8 in and the same cut divides into exactly five repeats and wastes nothing. A repeat four per cent larger costs fourteen inches per drop less.
Repeat waste is a sawtooth, not a slope. It is zero whenever the cut length is a multiple of the repeat and worst just above a multiple, and the peaks get taller as the repeat grows but the zeros never stop happening. So a larger repeat has a worse worst case and exactly the same best case. The practical consequence is that the hem allowance is a lever: moving the header by an inch can drop a whole 18 in repeat off every cut, and across twelve drops that is 216 in — six yards.
Half drop, straight match, random
The page prints all three because the choice is not always yours and it is worth knowing what it costs. On the defaults a straight match is 19-1/2 yd and the half drop is 20-7/8 — the difference is the accumulated skips and nothing else. A random match is 11-3/8 yd, a long way below both, because it drops the vertical rounding and the horizontal trim at the same time.
What the page cannot tell you is which one your fabric actually is. That is written on the bolt label or the memo sample, and if it is not, the supplier knows. Guessing random on a fabric that turns out to be a half drop is the error that ends with a seam nobody can stop looking at.
Where this is still a floor
There is no centring in this model. If the motif has to sit in the middle of each panel, the cutter no longer takes whichever repeat comes next off the roll — the starting point is fixed, and the cloth between one panel start and the next goes in the bin. That can cost another full repeat per drop and the calculator has no way to know whether your design demands it.
There is also no allowance for a bolt struck off grain, which is common enough on a printed cotton and which forces the cutter to follow the print rather than the weave. Order the memo, put a yard on the table, and look at where the design sits against the selvage before you commit to a quantity.
Questions people ask
How much extra fabric does a pattern repeat need?
For the panel in the form — 96 in wide, 84 in long with 10 in of header and hem, on 54 in goods with an 18 in vertical repeat and a 13.5 in horizontal one, half drop — it takes 20-7/8 yd against 11-3/8 yd for the same panel on a plain goods. That is 83 per cent more cloth, and it comes from three separate effects rather than one: the extra width the side match forces, the rounding of each cut up to a whole repeat, and the half-drop skips.
Does a horizontal repeat cost yardage?
Yes, and it does it in a way that hides. Each width has to be trimmed back to the last whole horizontal repeat so the design carries across the seam, which narrows the usable width without changing the length of any drop. The yardage per drop stays the same and the number of drops goes up. On the defaults that is 11.5 in off every width and one extra width for the panel.
What is a half drop repeat and what does it add?
A half drop means alternate widths sit half a repeat lower than their neighbours, so the design staggers across a seamed panel instead of lining up level. Cutting it means skipping half a repeat between one drop and the next, and that half repeat is a strip too short to use. On an 18 in repeat that is 9 in per gap, so a four-drop panel loses 27 in.
Is a bigger repeat always more wasteful?
No, and the page prints a counterexample from your own numbers. Waste is the gap between your cut length and the next multiple of the repeat, so it is zero whenever the repeat divides the cut evenly. On the default 94 in cut an 18 in repeat wastes 14 in while an 18.8 in repeat wastes nothing. A larger repeat has a worse worst case and the same best case.
Can I reduce repeat waste by changing the hem?
Often, yes, and it costs nothing to try. The rounding is done on the finished length plus the header and hem together, so moving that allowance by an inch or two can drop a whole repeat off every cut. Run the page at two or three hem allowances and see which side of a repeat boundary you are sitting on before you order.