One pair of curtains, or three?
That is usually the first real question about a bay window, and it is a design question rather than a measuring one. A bay gives you a curved or angled run of glass, several sections, corners, and often a sill, a seat or a radiator in the way. How you dress it changes how the whole room reads.
This article is about those decisions: what the hardware can and cannot do, where the curtains go when they are open, and how many of them there should be. The measuring itself is covered elsewhere, and it is worth reading before you order.
Decide the layout before the hardware
There are three common ways to dress a bay, and they suit different bays.
One pair, spanning the whole bay. The curtains follow the hardware around the bay and meet in the middle when closed. Open, they sit at the two outer ends. This gives the cleanest sweep of fabric and makes the bay read as one window. It needs the curtains to be able to travel round the corners, which is where passing brackets or a bent track come in, and it needs somewhere at each end for a lot of fabric to stack.
A pair to each section. Each window in the bay gets its own pair, so a three-sided bay ends up with three pairs. This suits deep bays with strong mullions between the sections, and it lets you close some and leave others open. It uses more fabric and shows more hardware, and the corners can look busy if the sections are narrow.
A pair across the front of the bay. The hardware runs straight across the room side of the bay, ignoring its shape, so when the curtains close the whole bay disappears behind them. This is the simplest option and often the right one when the bay is shallow, when there is a window seat you do not want covered, or when the curtains are heavy. It does mean losing the bay as a feature at night.
Look at the bay with the curtains shut and with them open before you decide. Both states matter, and people usually only picture one.
Pole, track, or a system built for bays
A standard straight pole will not follow a bay. What you need is either hardware designed to turn corners or hardware that ignores the bay entirely.
A bay pole system uses straight lengths joined at the corners with angled connectors, cut or set to your bay's angles. The pole stays visible and decorative, which is the point of choosing one. The detail that matters is how the curtain gets past each corner and each supporting bracket: passing brackets are shaped so rings can travel over them, and corner fittings have to let rings round the bend. If a system does not offer both, the curtains will stop at the first corner. The bay window poles are the place to compare systems rather than trying to adapt a straight one.
A bay track is bent to order, to the measurements of your own bay, so it follows the shape rather than approximating it. That covers square bays, splayed bays, bays whose angles are not equal to each other, and curved bays that no jointed pole will ever follow properly. You supply the measurements and the track is made to them. It can also be fixed to the ceiling where there is no wall above the glass, and it gives a smoother run with far less hardware on show. If the bay is curved, or the angles are unusual, or you want the fabric to do all the talking, look at the bay window tracks instead.
The trade-off is straightforward. A pole is the one you want people to notice. A track is the one you want people not to notice.
Stack-back is the thing people forget
Stack-back is the space the curtains occupy when they are fully open. In a bay it is the difference between a window that floods the room with light and one that is permanently half covered.
Bay curtains are wide. If a single pair spans the whole bay, that is a lot of gathered fabric to park at each end, and the ends of a bay are exactly where the wall usually runs out. Deeper headings and fuller curtains stack deeper still. If the bay ends flush into a corner or a return wall, the stacked curtain has nowhere to go except across the glass.
Two things help. Running the hardware a little past the end of the glass, where the wall allows it, gives the stack somewhere to sit. Splitting the treatment into sections spreads the bulk across several smaller stacks instead of two large ones. Both need thinking about at the planning stage, not after the curtains arrive.
What is already in the bay
Bays collect furniture. Check what the curtain has to live with before you fix anything.
A window seat or a fitted bench usually argues for curtains that stop at the seat, or for hardware across the front of the bay so the seat stays usable. A radiator under the bay window changes where the curtains should end. A deep sill will hold a curtain out from the glass unless the drop is planned around it. Table lamps, a desk, or a dining table pushed into the bay all affect whether floor-length curtains are practical at all.
None of this is about measuring. It is about deciding what the curtains have to do before you measure anything.
Then measure, carefully
Bays are the most common place for a measuring mistake, because a bay is several measurements rather than one, and the angles are rarely as tidy as they look. Once you have settled the layout and the hardware, work through the common mistakes when measuring bay windows and how to measure for a curtain pole before you order anything cut to size.
For ideas on how a finished bay can look, and how the layout choices above play out in real rooms, dressing a bay window is the companion piece to this one.
If in doubt, get it checked
A bay is the window most worth talking through with someone before you buy, because the corners, the angles and the stack-back all interact. The free design consultation exists for exactly this kind of window. Bring the shape of the bay, what is standing in it, and what you want the room to look like in the evening.