What Is Curtain Stack Back?
Curtain stack back is the amount of space your curtains take up when they are fully open. When drawn back, the fabric gathers at one or both sides of the window, creating a bundle of fabric known as the stack.
Getting this right matters because an undersized track means curtains cover part of the window even when fully open, reducing natural light. An oversized track wastes wall space and can look disproportionate.
The calculator above uses industry-standard stack back percentages applied to the finished track length, which gives a more accurate result than estimating from fabric width alone.
Key Principle
Stack back is calculated as a percentage of the track length, not the window width. This is why you cannot simply add 25% to your window measurement.
See why →Stack Back by Heading Style
All percentages are of finished track or pole length.
Pencil Pleat
Classic heading. Most fabric per metre, highest stack.
Eyelet
Popular modern style. Less stack than pencil pleat.
Triple Pinch Pleat
Elegant tailored look. Similar stack to pencil pleat.
Wave
80mm pitch gives smallest stack. Great for narrow reveals.
| Heading Style | Stack Back % | Best For | Track Required (200cm window) |
|---|---|---|---|
| Pencil Pleat | 25% | Traditional interiors, high fullness look | 267cm |
| Triple Pinch Pleat | 25% | Formal, tailored appearance | 267cm |
| Eyelet | 20% | Modern style, easy opening | 250cm |
| Wave 60mm | 23% | Contemporary, smooth folds | 260cm |
| Wave 80mm | 18% ✓ Best | Minimal stack, wide windows | 244cm |
Worked Example: 328cm Window, Pencil Pleat
Visual: how the 437cm track is used
Why You Cannot Simply Add 25% to Your Window Width
This is the most common measuring mistake. It seems logical to take your window width and add 25%, but the maths does not work because stack back is a percentage of the track length, not the window width.
328cm + 25% = 410cm track
Stack back on 410cm track = 102.5cm
Visible opening = 307.5cm
20cm of window still covered when open
328cm ÷ 0.75 = 437cm track
Stack back on 437cm track = 109cm
Visible opening = 328cm
Full window visible when open
The calculator above handles this correctly. Use it to avoid this mistake.
Frequently Asked Questions
What is curtain stack back? ▼
Curtain stack back is the amount of space your curtains occupy when fully open. The fabric gathers at one or both sides of the window, reducing the visible glass area. Knowing your stack back ensures you order the correct track length.
What affects curtain stack back? ▼
The four main factors are: heading style (the single biggest driver), curtain fullness ratio, track or pole width, and fabric weight. A heavy, densely-woven fabric will create a slightly bulkier stack than a lightweight voile, but heading style and fullness dominate.
Which curtain heading gives the smallest stack back? ▼
Wave curtains with an 80mm pitch require the least space at around 18% of track length, followed by eyelet curtains at 20%. If you have limited wall space beside your window, wave heading on a wave track is the most space-efficient option.
Does curtain drop affect stack back? ▼
Not significantly. A floor-length curtain and a sill-length curtain with identical heading and fullness will have very similar stack back. Heading style and fullness are far more influential than drop.
Do curtains need to clear the glass completely when open? ▼
No. Many customers deliberately allow the curtain stack to overlap the window frame slightly, which lets them use a shorter track while still achieving good light. If maximising light is a priority, use the calculator to size the track so the stack sits entirely off the glass.
How do I work out track length if I want to allow 10cm stack overlap? ▼
Calculate the track length for full clearance using the calculator above, then reduce by 20cm (10cm each side for a pair). This gives a track that leaves 10cm of curtain over the glass when open, which most people find acceptable and saves wall space.
Not Sure Which Track To Order?
Our team advises on track selection, sizing, and fitting every day. Get a free recommendation before you buy.
