First, decide where you want to place your window treatments:

Hang them several inches wider and higher than your window frame to make your windows look bigger.

For a cozier look, position the treatments a little lower or not as wide apart.

Show off an attractive window frame or molding: mount shorter curtains on a tension rod inside the window frame.

Then, measure for the perfect fit:

1. Determine the width. For full curtains, use twice the width of the window in fabric; for more casual curtains, use one and a half times the width. If you can't find the right width, sew two panels together.

2. Check that you'll have room for the hardware. Rods normally extend four inches beyond each side of the window. And install the hardware about five inches above the window frame.

3. Figure out the height you want. Curtains should hang either (A) four inches below the windowsill, or (B) a half inch from the floor (or just skimming the floor) or (C) in a "puddle" on the floor (in this case, add 6 to 10 inches to the distance from the rod to the floor). Shorter treatments, like cafe curtains, may graze the top of the windowsill or fall a few inches below it.