How to Measure Curtains for Bay Windows? | Section-by-Section Method

Measure a bay as one flat window and the curtains fight the angles, bunch at the corners, and cover glass you paid for. The fix: measure every section on its own, add the outer allowances, then drop the tape from the fixing point to where you want the fabric to finish. This works for two-angle, three-angle, and four-angle bays, and takes about fifteen minutes.

Gather the Tools and Set the Plan First

Use a metal tape measure—cloth tapes stretch and corrupt every number. Add paper and a pencil, and record each measurement immediately.

Settle two questions first, because both change your numbers:

• Inside or outside the recess? Curtains inside the bay sit within the angled walls; curtains in front run straight across the opening. Dunelm’s buying guide treats these as different measuring jobs, and the widths are not interchangeable.
• Pole or track? A pole is measured excluding the finials. A track is measured across its full length, including any center overlap where the two curtain halves meet.

Measuring Each Section, Angle to Angle

Start at the left end and work right, measuring each flat section from one angle to the next. Each number goes on paper separately—do not add as you go.

1. Hold the tape’s hook at the first angle where the wall turns.
2. Run the tape to the next angle and read the exact width.
3. Write that section down, labeled by position.
4. Repeat across every remaining flat section.
5. Total the individual widths to get the full span.

Adding the pieces can produce a total that differs by a few centimeters from one continuous sweep, and the piece-by-piece number is correct—angles take up real space a flat measurement ignores.

Stack-Back Allowance: The Step Most People Skip

Stack-back allowance is extra width at the outer ends so the fabric gathers beside the window instead of over it. Common guidance puts it at roughly 20–30 cm per outer side, or about 15–20 cm each side where wall space is tight. Take the larger figure when you can—a curtain that opens across the glass can’t be rescued by rehanging it.

The drop and mounting height decide how the finished thing looks. Measure the drop from the actual fixing point, just above the pole or track, down to your finish line: above the floor, kissing it, or with a slight break. With uneven floors, take several measurements and build to the longest, then position hardware to leave roughly 12–15 cm of clearance above the window where headroom allows.

Where the Hardware Has to Go

Tight headroom is the most common surprise in bay installations. Rule of thumb: if there’s 15 cm or more between the window top and ceiling, wall or ceiling brackets both stay open. Below 15 cm, a ceiling-mounted bracket or track is often the only option that fits.

Take your drop measurement from the bracket position you’ve settled on, not an assumed viable spot. Bays with little clearance are also where heavy curtains cause the most trouble, so if you’re still choosing fabric, our roundup of the best curtains for bay windows covers which styles hang well in a tight recess.

For the manufacturer’s own wording on pole versus track measuring, Dunelm’s guide on measuring for curtain tracks and poles lays out the overlap and finial details.

Mistakes That Cost You the Whole Measure

• Measuring the bay as one continuous flat window instead of section by section.
• Running the tape along the sill line rather than the exact pole or track line.
• Forgetting finials on a pole or overlap on a track.
• Omitting stack-back allowance, so open curtains block the glass.
• Using a fabric tape that stretches.

Hardware you order later must match today’s numbers, so double-check the total span and drop before committing. If your mount sits at the ceiling and the bay is deep, confirm your bracket choice against the clearance rule above before ordering.