Curtain width, fullness and stack-back

Fullness: what each ratio looks like#

Fullness is the ratio of flat fabric width to the finished width it covers. It is the only variable that decides whether a curtain looks like a curtain.

1.5x is the floor. Closed, a 1.5x panel shows shallow, wide folds and the weave reads as a plane rather than a drape. On a patterned voile that is fine and often intended. On a plain lined cotton it looks like a bedsheet on a wire, and no amount of good fabric rescues it.

2x is the standard and the right default. The folds hold their own shape when the curtain is drawn, the panel has enough body to fall vertically rather than flare, and the cost is predictable.

2.5x to 3x is what hand-finished headings need. A three-fold pinch pleat consumes a fixed amount of fabric in each pleat, so at less than about 2.5x the flat spans between pleats run out of slack and the curtain goes tight and scalloped when closed. Goblet pleats want 2.5x minimum. Sheers made to look genuinely full, rather than merely translucent, go to 3x.

There is a ceiling as well as a floor. A heavy interlined velvet at 2.5x on a 100 in (254 cm) rod produces a stack you cannot get out of the way, which is the subject of the rest of this page.

The panel arithmetic#

Three steps, no judgement required.

finished width = rod width + (2 x return) + overlap

flat fabric = finished width x fullness

panels = flat fabric / 50 in, rounded up (and up again to an even number for a pair)

Returns are the wrap-around at each end, from the rod face back to the wall: 3 to 4 in (8 to 10 cm) for a rod on standard brackets, 4 to 5 in (10 to 13 cm) for a track over a blind. The overlap is where the two leading edges cross at the centre: 2 to 4 in (5 to 10 cm), and about 3.5 in (9 cm) on a traverse rod with a master carrier. Both are finished dimensions, so they get multiplied by the fullness along with everything else.

Rod width	Finished width with returns and overlap	Flat fabric at 2x	50 in panels needed	Buy as a pair	Fullness delivered
48 in (122 cm)	58 in (147 cm)	116 in (295 cm)	2.3	2	1.7x
72 in (183 cm)	82 in (208 cm)	164 in (417 cm)	3.3	4	2.4x
90 in (229 cm)	100 in (254 cm)	200 in (508 cm)	4.0	4	2.0x
120 in (305 cm)	130 in (330 cm)	260 in (660 cm)	5.2	6	2.3x
144 in (366 cm)	154 in (391 cm)	308 in (782 cm)	6.2	6	1.95x

Returns of 3.5 in (9 cm) each and a 3 in (8 cm) overlap. Note what the ready-made width does to you: the 48 in rod lands at 1.7x and the 72 in rod at 2.4x, because 50 in comes in one size only. This is the strongest practical argument for made-to-measure. Custom curtains are cut to width, so you get the ratio you asked for instead of the ratio the nearest multiple of 50 in permits. Sheers are often sold at 54 to 60 in (137 to 152 cm) wide precisely to make the higher ratios affordable.

Stack-back is what sets the rod length#

The advice to extend a rod "4 to 10 in past the trim" is a floor dressed up as a rule. The real question is where the fabric goes when the curtain is open, and that is stack-back: the band of wall a gathered panel occupies at each end.

Stack-back scales with the width the panel covers when drawn, which is half the rod on a pair. Write that fraction as c and the rod length follows in one line:

rod width = clear width / (1 - c)

where clear width is the opening you want left uncovered, usually the casing width, sometimes just the glass.

Heading, 2x fullness	Stack as share of covered width (c)	Stack each side, 60 in window	Rod width	Stack as share of flat fabric
Grommet or eyelet	25%	10 in (25 cm)	80 in (203 cm)	13%
Wave or ripplefold	28%	12 in (30 cm)	83 in (211 cm)	14%
Rod pocket	30%	13 in (33 cm)	86 in (218 cm)	15%
Pinch pleat, 3-fold	33%	15 in (38 cm)	90 in (229 cm)	17%
Pinch pleat at 2.5x	38%	18 in (46 cm)	97 in (246 cm)	15%
Goblet pleat at 2.5x	40%	20 in (51 cm)	100 in (254 cm)	16%

Grommets stack tightest because the fabric folds around a rod of small diameter with nothing between the folds. Pinch and goblet pleats stack widest because each pleat is a stiffened bundle of three or four fabric thicknesses that will not compress. Wave and ripplefold sit in the middle but are the numbers to trust: the fold pitch is fixed by the snap tape or carrier spacing, so the stack varies from the calculation by well under an inch, where a hand-pleated curtain can vary by two.

Returns, overlap and the sides nobody photographs#

A return is not decoration. It closes the light gap at the end of the rod and stops the panel edge standing proud of the wall like a flag. Without one, a rod on 4 in (10 cm) brackets leaves a 4 in slot of daylight down each side of a "closed" curtain. Rods with elbow returns, wrap-around rods and tracks with a bent end all solve this; a plain rod with finials does not, which is why finials and blackout rarely go together.

The overlap at the centre matters for the same reason. Two panels that merely meet will part by an inch under their own weight and show a vertical line of light. 2 to 4 in (5 to 10 cm) of overlap, built into the finished width, holds the join closed. If your priority is darkness rather than looks, the whole problem is better solved with side channels or an outside-mounted shade, which is covered in inside versus outside mount for blinds and shades.

Single panel or a pair#

A pair is the default because it splits the stack. A single panel puts all the fullness and all the stack on one side: W = G / (1 - c) still applies, but with c against the whole rod rather than half of it, so a 48 in (122 cm) window with pinch pleats needs a rod about 72 in (183 cm) long and gives up 24 in (61 cm) of wall on one side.

Use a single panel where the wall is asymmetric and honest about it: a window tight into a corner, a window beside a door, a run of windows where the panels only need to close at the ends. Use a pair everywhere else. A single panel on a symmetrical wall reads as an unfinished pair.

What linings do to the numbers#

Lining changes both dimensions of the stack, and the depth is the one people forget.

Construction	Stack-back, added	Stack depth from the wall
Unlined cotton or linen	baseline	3 to 4 in (8 to 10 cm)
Cotton sateen lining	+10%	4 to 5 in (10 to 13 cm)
Three-pass blackout lining	+20 to 25%	5 to 7 in (13 to 18 cm)
Interlined with bump	+30 to 40%	7 to 9 in (18 to 23 cm)

The depth column decides two things. It tells you the rod projection you need to clear a blind or shade underneath, typically 3 to 5 in (8 to 13 cm) of bracket, and it tells you how far the open curtain intrudes into the room. An interlined pair at 9 in (23 cm) deep either side of a window narrows the usable floor in front of it by a foot and a half, which is worth checking against the walkway widths if the window is on a circulation route.

Working the numbers backwards#

Most of the time you do not get to choose the rod length. A wall runs out, a return wall gets in the way, or a radiator sets the bracket position. Solve in this order.

1. Measure the wall you actually have, corner to corner or obstruction to obstruction. That is your maximum rod width.
2. Subtract the clear opening you want. Halve the remainder. That is the stack you can afford per side.
3. Divide by half the rod width. That gives you c, the stack coefficient you have to hit.
4. Read c back off the heading table. If it lands at 25%, you need grommets or wave. If it lands at 33% or more, you can have pinch pleats.
5. Only now fix the fullness, then divide by 50 in to get the panel count.

If step 3 gives you c under about 22%, no heading will do it and you are choosing between covering some glass, moving to a shade, or fitting a stationary panel on one side only. That is the point to stop specifying curtains and read blind and shade sizing instead. Once the width is settled, curtain length and hanging height sorts the vertical, and the proportion rules explain why a wide, high-hung pair reads better than a narrow, tall one at the same fabric cost.