How to Measure for Curtains, Including the Part Most People Skip

Five measurements decide a curtain, and four are obvious once you know to take them. The fifth decides whether the curtains can open at all, and it is almost never taken before the order goes in.

Where the rod goes

The rod position sets everything downstream, because the drop is measured from it. Three numbers:

• The window head to the intended rod position — this is the drop, and it is not a standard size.
• The rod span, edge to edge, which sets fullness and therefore how much cloth you need.
• The return, how far past each side of the frame the rod extends. Three to six inches is usual, and it is what lets the panels clear the reveal when open.

Set the rod wider than the window and the panel covers the frame edge when closed, removing the lit strip beside the glass. Set it narrower and the curtain sits inside the reveal, looks narrow, and lights the frame edge on both sides. The mounting height is the same decision drop length and ceiling height works through.

Two practical constraints. The bracket needs solid fixing — into a stud or a suitable anchor, not plasterboard alone, because a loaded curtain pulling outward is a real load. And check clearance for a ceiling fan or deep cornice.

How the hem lands

Two positions, not one. Just at the floor, where the break is a clean line, or pooling slightly. The failure case is stopping short: a curtain ending two inches above the floor looks like it is missing something, and makes the window look shorter than it is.

Where you want the hem depends on traffic and cleaning. A hem touching the floor in a room with hard flooring collects dust at the break and needs a vacuum run along it. A hem clearing the floor by an inch wipes clean and looks deliberate.

The part most people skip

Where the curtains go when they are open. A gathered panel does not compress to nothing — it stacks to roughly one and a half times the width of one panel. Two 63-inch panels on a 60-inch window give about 190 inches of gathered fabric, compressing to roughly 95 inches of wall.

That is the number that catches people. It has to fit on one side, or split across two, measured from the frame edge to whatever is in the way: a radiator, a door frame, a corner, a tall piece of furniture. On a narrow window with a radiator under it the curtains may only open halfway, and no fullness setting fixes that.

The second thing people skip is the wall above the rod. On a rod mounted below the ceiling there is a band of wall that no fullness fills, and it is why a high ceiling makes a window look larger.

Inside the frame or outside it

Three mounting positions, trading against each other:

• Inside the reveal, where the curtain sits in the recess. Takes least space, gives least light, and shortens the drop because the recess has depth.
• On the wall just outside the frame, the usual position. Maximises the drop and lets the panel overlap the frame edge.
• On the ceiling or into a soffit, where the track runs up into a recess. The curtain reads as full height and the gap above it disappears.

The choice is a function of the wall beside the window, not of the window. Measure the stack space first, then pick a position that leaves room for it.

What to measure, in order

1. Window width, frame edge to frame edge, and the reveal depth.
2. Window head to the intended rod position, plus ceiling clearance.
3. Rod span, once the return is added to each side.
4. Intended hem position relative to the floor.
5. The wall space beside the window for the stack, and what stands in it.

Take those five and the panel count, width and finished length stop being estimates. What remains is fullness, and the ratio of cloth to span that sets it is in curtain width and fullness.