Stack-back & clearance, explained
Stack-back is the single measurement most people leave out, and the one that decides whether a window looks full of light or half-curtained. Here is how to get it right.
Stack-back is the space the curtain takes up when it is open. Get it right and the open curtains rest neatly on the wall, leaving the whole window clear; get it wrong and even beautiful fabric on the finest pole will sit across the glass, cutting the light and making the window look mean. It is the most commonly skipped step in measuring, and the easiest to fix.
Why it matters more than people think
A window's job is light. If the open curtains cover 30cm of glass on each side, that is 60cm of daylight gone every single day. On a 1.5m window that is a fifth of the view. The whole point of a generous pole length is to push that fabric off the glass and onto the wall, which only works if you measured for it.
How much to allow
As a working starting point, 15 to 20cm each side of the glass for a standard pair. But stack-back is not one number. It grows with the fabric:
- Light, unlined curtains: stack tightly; the lower end of the range is fine.
- Lined or heavier fabric: more bulk, more stack; move toward the upper end.
- Interlined curtains: considerably more; allow extra again, as the interlining doubles the gathered depth.
- Wider windows: think in proportion. A rough guide is 12 to 18 per cent of the glass width for the pair; the wider the glass, the more absolute room the fabric needs.
The heading also changes the sum, because a flat wave gathers differently from a deep pinch pleat. Our heading styles guide sets out how each one behaves.
A return wall, a radiator below the window, a light switch or a door swing can all steal the space the curtain needs to stack into. Check the obstructions before you set the pole length, not after the brackets are up.
Clearance: the other half of the job
Stack-back is about width. Clearance is about everything around the window:
- Above: room for the heading, rings and finials between the pole and the ceiling, plus the bracket projection.
- In front: the bracket has to hold the curtain clear of handles, trickle vents and a projecting sill. Deep sills or recessed handles may call for a longer bracket or a different fixing.
- Below: a radiator under the window affects both the drop you choose and how the curtain hangs; a sill-length curtain is often the honest answer there.
Settle stack-back and clearance together and the rest of the order falls into place. If the window is a long run of glass or a set of doors, the maths shifts again. See measuring for bi-folds and large glazing.
Common questions
What is stack-back?
Stack-back is the space a curtain occupies when fully open and gathered to the side. Allowing for it in the pole or track length is what lets the open curtain sit on the wall rather than across the glass.
How much stack-back should I allow?
As a starting point, 15 to 20cm each side of the glass for a typical pair. Fuller headings, heavier fabric and lining all increase it; a rough guide is 12 to 18 per cent of the glass width for the pair, more for interlined curtains.
Does the heading change the stack-back?
Yes. A flatter wave heading stacks tighter and more predictably; deep pinch pleats and heavily gathered pencil pleats take more room. Lining and interlining add bulk and therefore stack.