How to Measure a Five-Sided Bay Window for a Curtain Track
If you’ve got a five-sided bay with a deep window sill, this quick guide shows you exactly how to measure for a ceiling-fixed curtain track designed for sill-length curtains. Easy steps, clear examples, and total peace of mind.
This setup works brilliantly where the sill is too deep for floor-length curtains to hang cleanly in front of it. Instead, your curtains finish neatly just above the sill and stack back on the small side walls inside the bay when they’re open.
How to Measure a Five-Sided Bay Window for a Curtain Track
If you’ve got a five-sided bay window with a deep window sill, this guide is for you. Here I’ll show you exactly how to measure for a custom-made curtain track that fixes to the ceiling inside the bay and carries sill-length curtains.
This setup works brilliantly where the sill is too deep for floor-length curtains to hang cleanly in front of it. Instead, your curtains finish neatly just above the sill and stack back on the small side walls inside the bay when they’re open.
This method can be used for:
- Single or double curtain tracks
- Ceiling-fixed tracks only
- Five-sided bays with deep sills
- Sill-length curtains that sit just above the window sill
If your bay has a shallow or no sill and you’d prefer floor-length curtains, there will be a separate guide for that setup too.
When this guide is right for your window
Use this guide if:
- Your bay has five sections (three across the front and two angled sides).
- You have a deep window sill that would clash with floor-length curtains.
- You want sill-length curtains that finish just above the sill.
- You’ll be ceiling fixing the track inside the bay.
- When open, you’re happy for the curtains to stack onto the small side walls inside the bay.
Because the curtains are stacking on those small side walls (A–B and E–F), they may also cover some of the glass on the side windows — especially if the side walls are quite narrow or your curtain fabric is thick or heavily lined.
That’s perfectly normal for this type of bay. It’s a trade-off between having sill-length curtains and having a very deep sill. You can always mention this in your enquiry if you’re unsure, and I can advise based on your bay photos.
Quick video: measuring a five-sided bay window
Sometimes it’s easier to see it done. Watch this short video to see where to put your measuring points and how to work around the deep sill.
Overview
Let me show you quickly how to measure your five-sided bay window for a custom-made curtain track that will fix to the ceiling within the bay. In this example, we’re looking at sill-length curtains, but the same measuring method can be used for both single and double curtain tracks.
Step 1 – Add measuring points to your bay
First, you’ll need to add measuring points to your bay window. The easiest way is to use small Post-it notes at each point, each marked with a letter. This makes it very simple and quick to measure accurately from point to point.
In the video, you’ll see these measuring point letters appear in red on the bay. We’ll be using:
- A, B, C, D, E and F around the shape of the bay, including the small side walls.
Step 2 – Measure along the back of the window sill
You’ll take all of your sizes by measuring along the back of the window sill, where it meets the bottom of the window frames, plus the width of the little side walls at A to B and E to F.
Simply measure following the yellow arrows as they appear in the video, going:
- A → B
- B → C
- C → D
- D → E
- E → F
Measure between each lettered point and then add each size into its own box on the final sizes form.
Step 3 – Measure straight across the bay
Once you’ve taken all your sizes around the bay and the returns on each side, the next step is to measure straight across your bay from wall to wall.
Measure from point A to point F. This gives us the overall width across the back of the bay and helps confirm the shape when we set it out full-size.
Step 4 – Measure the diagonals
Finally, take the diagonal measurements. These are important because they help check that all of your other sizes make sense when we draw the bay out.
Measure the diagonals as follows:
- From A → D
- From A → E
- From F → B
- From F → C
Wrap up
That’s all there is to measuring this style of five-sided bay window for a ceiling-fixed curtain track. Once you’ve got all of those measurements written down and labelled clearly, you’re ready to fill in the form and send everything over.
And as always, if you have any questions at all while you’re measuring, please just ask — I’m very happy to help.
Step-by-step: how to measure your five-sided bay
Step 1 — Mark your measuring points (A to F)
To keep everything organised, I recommend labelling your measuring points along the back of the window sill, where it meets the bottom of the window frames.
Use small Post-it notes or masking tape and mark them:
A – B – C – D – E – F
These points follow the shape of the bay:
- A and F – the small side walls at each end
- B, C, D – the three main front sections of the bay
- E – the other angled side
All of your measurements will be taken from point to point along the back edge of the sill, which is where the ceiling-fixed track will line up with the window below.
Step 2 — Measure each section of the bay
With your points marked, measure:
- A → B
- B → C
- C → D
- D → E
- E → F
Make sure you’re measuring from the back of the window sill (where sill meets frame), following the angle of each section.
If your bay has little return walls inside the bay at A and F, those lengths (A–B and E–F) are especially important, because this is where the curtains will stack back when they’re open.
Write each size down clearly and keep the labels consistent with the form you’ll be filling in.
Step 3 — Measure straight across the bay (A to F)
Next, measure straight across the bay from:
A → F
This is the wall-to-wall span across the back of the bay at sill level. It helps confirm the overall width and shape when we set your bay out full-size on the workbench.
Step 4 — Measure the diagonals
Finally, measure the diagonals. These help us confirm all the angles and catch any numbers that don’t quite add up.
Measure:
- A → D
- A → E
- F → B
- F → C
Think of this as a “sanity check”. If one size is out by too much, it will show up clearly when we draw your bay and compare it to your photos.
How your curtains will sit when they’re open
Because this guide is for deep-sill bays with sill-length curtains, the track will follow the ceiling inside the bay and the curtains will:
- Hang close to the glass, following the shape of the bay.
- Finish neatly just above the top of the window sill.
- Stack back onto the small side walls (A–B and E–F) when open.
Depending on:
- The width of those small side walls, and
- The thickness and fullness of your curtain fabric,
the stacked curtains may cover some of the glass on the side windows. This is perfectly normal with deep-sill, sill-length setups and is often the best compromise between:
- Keeping the curtains inside the bay,
- Avoiding them crashing into a deep sill, and
- Still being able to open and close them smoothly.
If minimising glass coverage is important to you, mention it when you get in touch and I can talk through options.
What if I want floor-length curtains in a five-sided bay?
If your bay has a shallow sill or no sill at all and you’d prefer floor-length curtains, the setup and measuring method are slightly different. We will be building a new page for this situation very soon.
Frequently asked questions
Because this guide is specifically for five-sided bays with deep window sills. With a deep sill, floor-length curtains can’t hang in front cleanly — they end up pushed forward or bunched over the sill. Sill-length curtains give a much neater, more practical finish for this type of bay.
They might, yes — especially if the small side walls (A–B and E–F) are quite narrow and you’re using thick or interlined curtains. When the curtains are stacked open, they sit against those small side walls and can cover a portion of the side glass. This is normal for deep-sill, inside-bay setups and is usually a good trade-off for a neat look and easy operation.
You can, but if you’re planning on floor-length curtains, you’ll probably be better with the floor-length version of this guide. Shallow sills give you more flexibility on where the track can sit and how the curtains hang.
Yes. Always measure from the back edge of the sill, where it meets the window frames. That’s the reference line we use when we draw out your bay and bend the track, regardless of how deep the sill is.
That’s absolutely fine — most aren’t. The whole point of taking section sizes and diagonals is so we can bend the track to match the exact shape of your bay, not some “standard” template. As long as your measurements are accurate and clearly labelled, we can work with it.
For bays, we often spot measurement issues when we draw your shape out full-size and compare it with the photos you’ve sent. If anything looks odd, we’ll check with you before making the track.
If you’re unsure, just take clear photos of the bay, mark your labels A–F in the pictures if you can, and send them with your measurements. I’ll happily look over everything and confirm you’re on the right track before we go ahead.
Next Steps
If you’re at the stage where you want to choose your track, great — you can browse all the options below.
If not, feel free to send me a photo of your bay and I’ll happily tell you exactly what will work best.