How to Measure for Bay Window Curtain Rods? | Wall Widths, Not Glass

Measure each wall section of the bay separately — inside corner to inside corner — along the exact line the rod will sit, then order for the total wall span, not the window glass.

Two of the three walls come back the same width, and the third one is off by half an inch. That half inch is why custom bay rods arrive too short, and it disappears the moment you record every section on its own instead of trusting the symmetry of the windows.

Bay rods follow the walls the brackets mount to, so the wall is what you measure. Grab a steel tape, a level, and a notepad. Fifteen minutes now saves a return shipment later — and the section-by-section method below works for three-sided, five-sided, and curved bays alike.

What Do You Actually Measure On A Bay Window?

You measure the back wall from inside corner to inside corner, then each side wall from its inside corner to wherever the rod should end — usually just past the window frame. The width of the glass tells you nothing useful, because the rod has to travel the wall line, including the corners.

Finding that wall line matters as much as the numbers. Iron Hardware’s measuring guide tells customers to pick an uninterrupted horizontal band where the brackets will land, then run the tape along that same band across all sections. Mark a corner point on each side and measure 24 inches outward to calculate the corner span some custom makers require.

Run a level under the tape as you go. Floors and ceilings in older homes drift, and a tape that climbs or dips will hand you a width that doesn’t match the wall you’re drilling into.

• Back or center section: inside corner to inside corner, at bracket height.
• Left side section: from the inside corner to the intended rod end.
• Right side section: measured on its own — never copied from the left.
• Multi-sided bays: keep going around. Five-sided bays need every wall length plus each corner span.

Curved bays break the straight-tape approach. Drapery Rods Direct’s bay window guidance says to capture the width from one side of the wall to the other, then measure the curve depth with a taut string or soft tape laid along the arc — or send the maker a string trace of the curve. A rigid tape bridging the bend reads short, every time.

How Much Extra Room Do Finials, Returns, And Blinds Need?

Budget the hardware before you order: finial length, return clearance, and the projection of any blinds still on the window all eat into the rod’s usable width. Buy the length that clears all three, not the length of the wall alone.

Finials are the most common miss. Several rod makers warn that decorative ends add real width, so a rod ordered to the exact wall span can come up short once the finials are screwed on. If you’re going with a French return, Iron Hardware recommends at least 3 inches of clearance past the outside end of the return so the curtain can wrap around it cleanly.

Existing blinds raise a second question: how far does the headrail sit off the wall? Measure that projection and check it against your bracket depth, or the rod will sit proud of the window with a gap behind it. Mounting above the molding instead? Measure the bracket clearance height first. Ceiling-mounted curtains change the job entirely — you measure the ceiling sections, not the walls. A digital protractor is a quick way to capture the angles of a bay accurately when you’re ordering a custom system.

How Wide Should The Curtains Be For A Bay Window?

Plan for fullness of roughly 1.5 to 2.5 times the rod width, and add extra on the outer ends so curtains can stack clear of the glass. A 36-inch rod that hangs flat needs at least 54 inches of fabric; 72 inches gives medium fullness and 90 inches reads fuller still.

If the rod isn’t chosen yet, add 1 to 3 inches on each side of the window when picking width. Wanting a wider, more generous look with better light control? Livingetc’s guide to choosing curtain rails suggests 3 to 6 inches past the frame per end.

Return rods need their own math. Drapery Rods Direct advises adding 5 to 10 inches of stack width on the outer side of a bay so the curtain has somewhere to gather when it’s pulled open.

Once your numbers are down, the rod itself is the easy part — our roundup of tested bay window curtain rods covers shapes and bracket types that suit three-sided and curved bays. Before ordering any custom system, it also pays to measure bay windows for drapery rods the way the custom makers themselves instruct, since their ordering forms assume you’ve already captured corner spans.

Frequently Asked Questions

Do I measure the window glass or the wall?

The wall. The rod mounts to the wall and follows it around the corners, so wall dimensions are what determine the rod length you need. Measuring the glass leaves you short at every corner, and often short at the outer ends too. Record the wall sections at bracket height, then add finial and return allowances on top.

Why did my two side walls measure differently?

Because bays are built by hand, and walls that look symmetrical rarely are. Framing, drywall thickness, and corner finishing all shift by fractions of an inch. Measure each section independently and write the numbers down as you go. Ordering to the assumption of equal sides is one of the most frequent mistakes in bay window measuring.

What if my bay window is curved?

A straight tape won’t follow the arc, so it reads short. Run a soft tape or a taut string along the curve to capture the depth, and measure the overall wall width from side to side. Many makers of curved bay rods accept a string trace of the curve instead of a single number, which sidesteps the guesswork entirely.

How much curtain fabric do I need for a bay?

Start at 1.5 times the rod width for minimum fullness and work up to 2.5 times for a fuller drape. Then add stack width on the outer ends — 5 to 10 inches with return rods. That extra lets the curtains gather clear of the glass instead of blocking half the window when they’re open.