How to Choose the Right Size Tension Curtain Rod for Your Window

Measure the inside width of your window casing, then buy a rod whose range extends 1–2 inches beyond that span.

For the full breakdown, see our best 70 Inch Tension Curtain Rod guide.

Choosing the right size tension curtain rod comes down to one measurement and one rule: the rod must sit slightly longer than the opening, not exactly equal to it. The spring tension that holds the rod in place needs room to compress, so a rod that barely reaches is a rod that will slip. Get the sizing right and installation takes under a minute, no tools, no holes.

Measure the Window Opening First

For an inside-mounted tension rod, measure the inside width of the window casing where the rod will sit — never the outside trim. Run the tape measure from the inner edge of one side to the inner edge of the other, at the height where the rod will rest.

Older windows are rarely perfectly square. Take three measurements — near the top, middle, and bottom of the opening — and use the average if they differ. This keeps you from buying a rod that fits the top but sags at the middle.

Write that number down. It’s the single figure every other sizing decision hangs on.

Match the Rod’s Range to Your Span

Every tension rod lists an adjustable range, like 28–48 inches or 80–92 inches. That range is the ground floor of compatibility: your measured opening must fall inside it. But Home Depot’s sizing advice is explicit that the rod should be “slightly longer than the space it spans” — roughly 1–1.5 inches longer than the gap before you compress and install it.

Why? The spring needs that extra length to generate the pressure that grips the window frame. A rod set to exactly the opening width has almost no spring tension left — it will slip the first time a curtain brushes against it.

These larger allowances exist because longer rods flex more under load. The extra tension compensates for that flex, keeping the rod pressed firmly into the frame. For typical window widths — 28 to 72 inches — the simpler 1–1.5 inch rule works fine.

Diameter and Weight Capacity Matter

Rod diameter determines what the rod can hold. If you’re hanging anything heavyweight, check the weight rating on the package — tension rods have limits, and exceeding them means sagging or a sudden collapse.

Tension rods are genuinely best for sheers and lightweight curtains. As span increases, holding strength declines. A 50-inch window with a sheer curtain is a comfortable pairing; a 110-inch span with heavy velvet is asking for trouble. If you need to cover a wide opening with heavy fabric, a ceiling-mounted track or a traditional rod with brackets is the safer route.

Some sources also suggest using the average of your three measurements when the window isn’t square — this single number is what you compare against the product’s adjustable range. If your average falls at the very edge of a rod’s range, size up to the next range and extend it further.

Install: Compress, Position, Release

Once the rod range fits your opening, installation is straightforward.

1. Extend the rod so it’s slightly longer than your measured width — about 1–1.5 inches for most spans.
2. Compress the rod by pushing the ends together.
3. Position it inside the window frame so the end caps rest flat against both sides.
4. Release slowly. The spring expands, pressing the caps into the casing.
5. Lock or tighten per the product instructions so it holds.

If the rod feels loose after releasing, extend it a bit more and try again. If it bows in the middle or won’t compress enough to fit, you’ve got the wrong range — swap it before hanging anything on it.

When you’re ready to buy and want a rod vetted for a specific span,

Common mistakes come down to three: buying a rod whose range barely covers the opening, measuring the trim instead of the inside span, and loading a slim rod with curtains it wasn’t built to hold. All three are easy to avoid with the numbers above.