How to Measure for 108 Inch Blackout Curtains: Getting the Length and Width Right

For 108-inch blackout curtains, measure width from the rod or track span and length from the rod’s top to your desired hem — usually the floor.

The 108 on the package is a length, never a width. Home Depot lists it among the standard curtain lengths, and retail packaging puts width first, length second. That single mix-up is why so many people end up with panels that look full on the rod but leak a bright stripe at the edges.

Blackout performance is a measurement problem before it’s a fabric problem. Rods that stop at the window frame and panels sized to the glass leave the light two easy paths in. Below is the order that closes them.

How Wide Should the Rod and Panels Be?

Start with the rod span, not the glass. Measure your window’s outer trim, then add a few inches of extension past each side — a common retail recommendation is 3 to 6 inches per side. That overhang is what kills the glow at the edges.

The rod’s height matters too. Home Depot advises hanging it a few inches above the trim, up to a few inches below the ceiling. Mounting higher also raises the light gap you’re trying to seal, so decide the height before you measure anything else.

Once the rod is sized, apply fullness. Blackout guides commonly cite a ratio of about 1.5x to 2x the rod width, with 2x to 2.5x for a heavier, more gathered look. Panels measured too close to the rod width go flat when closed and open gaps at the center seam.

The clearest blackout-specific mistake is sizing to the window opening itself. Fullness and overlap both disappear from that number, and blackout fabric can’t block light it never covered.

How Do You Measure Length Without Getting It Wrong?

Measure from the installation point — the top of the rod or track, not the top of the window — down to where you want the hem to land.

For blackout coverage, floor-length or floor-adjacent is the usual target. Floor-to-ceiling blocks the most light; roughly half an inch above the floor gives a clean floor-length look without dragging. Below-sill works in rooms where floor length is impractical, but it leaves more bleed at the bottom.

Floors lie. Marks & Spencer recommends measuring at three points across the window and using the shortest measurement, which keeps a hem from dipping into the floor on a low side. Do the same at each end and the middle.

One warning on ordering: a 108-inch panel is a fixed length. If your rod-top-to-floor distance runs longer, no amount of measuring saves that panel — adjust the rod height or pick a different length.

If you’d rather compare panels that already exist in the right size, this roundup of tested 108 inch blackout curtain options covers what actually ships in that length. For the official measuring method and standard length chart, Home Depot’s curtain measuring guide lays out the same rod-extension and fullness approach in detail.

What Changes on a Track or Room Divider?

Track-mounted and room-divider setups use the track length, not the window width. Measure each straight segment of a bent track separately and add them together.

Don’t cut a corner by measuring the gap between walls. A bent track’s total run is longer than that straight-line distance, and undersized panels on a divider gap are instantly visible from both sides.

Height still works the same way: from the track’s top edge down to your target hem, checked at more than one point.

Quick Reference: The Whole Order

1. Decide rod height — a few inches above the trim, or up toward the ceiling.
2. Measure the window’s outer trim, then extend 3–6 inches past each side for the rod.
3. Multiply the full rod span by 1.5x–2.5x to get total panel width.
4. Measure from the rod or track top down to the floor, taking three readings and keeping the shortest.
5. Match those numbers to a 108-inch panel — and if your length runs over, raise the rod or choose another length.