Bay windows account for most of the measuring queries we deal with, and the same handful of errors come up again and again. None are difficult to avoid once you know to look for them.
1. Assuming the corner angles are equal
This is the big one. People measure one corner, find it is 135 degrees, and assume the other matches. In a house built before the 1950s the two corners frequently differ by several degrees, and a bespoke bay pole made to the wrong angle will not sit against the wall.
Measure each corner independently with an angle finder, or by holding a piece of card into the corner, marking the angle and measuring it flat afterwards. Record them separately even if they look identical.
2. Measuring at sill level instead of pole level
In a splayed or curved bay, the width across the window narrows as you move up or down, because the walls are not parallel. Measuring along the sill and ordering a pole to that figure gives you something that does not fit the line it will actually occupy.
Measure along the exact line where the pole or track will sit — usually 10–15cm above the recess. Hold the tape at that height and follow the wall.
3. Forgetting the returns
The return is the section of pole that continues past the bay onto the flat wall on each side. It is what lets curtains stack clear of the glass when open.
People measure the three faces of the bay, order to that total, and end up with curtains permanently covering part of the window. Allow 15–20cm of return at each end where the wall permits, and include it in the total length you order.
4. Taking one drop measurement
Floors are rarely level, particularly in older houses, and a bay can vary by 2–3cm from one side to the other. Measure the drop at each face, and at both ends of a curved bay.
For floor-length curtains, work from the shortest measurement. A curtain that is slightly short at one end looks far better than one dragging on the floor at the other.
5. Ignoring what is in the way
Several things regularly get overlooked until the pole is up.
Window openers. Casement handles and top-hung openers need clearance. Check the window still opens fully with a pole in position.
Radiators. A radiator under a bay is very common. Floor-length curtains in front of it will trap the heat against the glass.
Coving and ceiling height. If you want the pole high, make sure there is room for the bracket and the ring above the pole.
Corner clearance. Curtains need somewhere to gather at each corner. In a shallow bay there may not be enough space, which changes what will work.
Before you order
Write down: the width of each face measured at pole height, each corner angle, the return at each end, the drop at each face, and any obstructions.
Take a photograph of the whole bay from inside the room. If anything looks unusual, send it to us with your measurements before ordering — a two-minute check is much cheaper than a bespoke pole made to the wrong dimensions.