How to Measure Room
Windows

How to Measure Windows for Curtains

Mount the rod 4-6 inches above the window frame and 4-6 inches past each side, then measure from the rod down to where you want the curtains to end — the floor, sill, or somewhere between.

To measure a window for curtains, you’re really taking two separate measurements: how wide the rod needs to be, and how long the curtains need to hang. Mount the rod 4-6 inches above the window frame and extending 4-6 inches past each side of the frame, then measure straight down from where the rod will sit to your chosen ending point.

Step 1: Decide on rod placement, then measure the width

Curtain rods aren’t mounted at the window’s own width — they extend beyond the frame on both sides so that, when open, the curtain panels stack outside the glass instead of covering it and blocking light.

  1. Measure the window frame’s outer width.
  2. Add 4-6 inches to each side (8-12 inches total) for the standard look, or 8-12 inches per side for a wider, more dramatic effect.
  3. That total is your rod length — this is also the number our curtain rod calculator is built around, if you’d rather not do the addition by hand.

Example: A 36” wide window frame, with 5” added on each side → 46” rod length.

Step 2: Decide on curtain length, then measure the height

First, pick where the rod will sit: 4-6 inches above the top of the window frame is standard (it makes the window look taller). Then measure straight down from that point to your chosen ending length:

Length style Ends at
Sill length The windowsill
Apron length A few inches below the sill/trim
Floor length (most common) About 1/2” above the floor
Puddle length 1-3” of fabric pooling on the floor

Example: Rod mounted at 60” from the floor, floor-length curtains → order panels rated for 59.5” length (leaving that half-inch gap above the floor).

Step 3: Check panel width, not just rod length

The rod length tells you how wide to mount the hardware — it doesn’t tell you how wide a fabric panel to buy. For curtains to look full and gathered when closed rather than flat, the combined width of both panels should be roughly 2 to 2.5 times the rod length. A 46” rod would want roughly 92-115” of total panel width, split across two panels.

A few things worth double-checking

  • Measure at multiple points. Window frames aren’t always perfectly square — measure width at the top and bottom of the frame and use the wider number.
  • Check for obstructions. Make sure the planned rod position clears any trim, blinds hardware, or nearby corners before drilling.
  • Confirm bracket depth. If you have deep window trim or blinds already installed, you may need rod brackets with extra projection so the curtains clear them.

Curtain Rod Length Calculator

Window width in, rod length and fabric yardage out.

Overhang style

Recommended rod length

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Frequently Asked Questions

How far past the window should curtains hang on each side?

4-6 inches past the frame on each side is the standard look, which lets curtains fully clear the glass when open (so they don't block light) and makes the window appear a bit wider. For a noticeably wider-window effect, some designers go 8-12 inches past each side — it's a style choice, not a fixed rule.

How do you measure curtain length?

Measure from where the rod will sit down to your chosen end point: the windowsill ("sill length"), just below the sill or trim ("apron length"), the floor ("floor length", the most common choice, ending about 1/2 inch above the floor), or pooling slightly on the floor ("puddle length", adding 1-3 inches beyond floor length). Floor length is the standard default if you're unsure.

How high above the window should curtain rods be mounted?

4-6 inches above the window frame is standard, and it makes the window and ceiling look taller. For rooms with high ceilings or a more dramatic look, some go higher — up to two-thirds of the way to the ceiling — but the rod should never sit lower than the top of the window frame.

How do you measure a bay window for curtains?

Measure each flat section of the bay separately, since they're rarely the same width, and decide whether you want one continuous rod bent to follow the bay's angles or a separate straight rod per section. Either way, apply the same 4-6 inch overhang rule at the outer edges of the whole bay, not at each individual pane.

Do you need extra fabric width for curtains to look full when closed?

Yes — for curtains to look gathered and full when closed rather than flat and skimpy, plan for the total fabric width (across both panels) to be 2 to 2.5 times the rod length, not equal to it. This is separate from the rod-length measurement itself, but it affects which panel width you should buy.

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