Do I measure the window or the trim for curtains?

For a rod on the wall, measure to the outside edges of the trim. For a rod inside the frame, measure the inside of the frame.

Should I measure the window width in more than one place?

Yes — at the top, middle, and bottom. Use the widest for an outside mount and the narrowest for an inside mount.

What is a curtain return?

The part of the curtain that wraps from the front of the rod back to the wall at each end, hiding the bracket and blocking light.

Do I need the rod before measuring for curtains?

It helps, because curtains cover the rod’s full width. If it isn’t chosen yet, plan its length first.

Is width more important than length?

Both matter, but they are measured separately. Width decides fullness; length decides where the hem falls.

Illustration of a tape measure across the outside edges of a window frame, with the rod span marked above it

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How to Measure a Window for Curtains

Measuring for curtains is quick, but the numbers that matter depend on how the curtains will hang. A rod inside the window frame and a rod on the wall above it need different measurements, and the rod and its brackets add measurements of their own. This guide covers what to measure and in what order.

Ready to try the tool this guide describes?

Open Curtain Width Calculator →

Measure the window

Use a steel tape, not a cloth one, which can stretch.
Measure across from the outside edge of the trim on one side to the outside edge on the other.
Measure at the top, middle, and bottom, and keep the widest reading.
For a rod inside the frame, measure the inside of the frame instead, at its narrowest.

Inside or outside mount

Inside or outside mount comparison
Mount	Rod sits	Width to use
Inside	Within the window frame	The frame’s inside width
Outside	On the wall above the window	The rod’s span, usually wider than the window

Measure the rod and returns

For an outside mount, the curtains cover the rod, so measure the rod bracket to bracket — or decide it as the window width plus the extension on each side. For a return, measure how far the rod stands off the wall at the bracket; that is how far the curtain wraps back at each end.

A note on length

Width and length are separate measurements. Length runs from the rod, or the top of the rings, down to where you want the hem: just above the floor, kissing it, or puddled. The Curtain Width Calculator only sizes the width.

Write it down before you shop

Window width (outside or inside, and which).
Rod width, bracket to bracket.
Return depth at each end, if any.
Height from the rod to the floor.

Measuring a Window for Curtains FAQ

Do I measure the window or the trim for curtains?: For a rod on the wall, measure to the outside edges of the trim. For a rod inside the frame, measure the inside of the frame.
Should I measure the window width in more than one place?: Yes — at the top, middle, and bottom. Use the widest for an outside mount and the narrowest for an inside mount.
What is a curtain return?: The part of the curtain that wraps from the front of the rod back to the wall at each end, hiding the bracket and blocking light.
Do I need the rod before measuring for curtains?: It helps, because curtains cover the rod’s full width. If it isn’t chosen yet, plan its length first.
Is width more important than length?: Both matter, but they are measured separately. Width decides fullness; length decides where the hem falls.