Measure the window before you fall for anything

Most returns in this trade start with a tape measure that stayed in the drawer. Ten minutes with one saves the whole errand.

Width first, and measure three times

Window frames settle with the house, so the top, middle and bottom of the same opening can differ by half an inch. Measure the width at all three heights and keep the numbers, because which one you use depends on where the piece will sit.

For anything going inside the frame, the narrowest of the three wins. For anything hanging in front of the wall, the widest is your floor, not your ceiling: curtains want extra room on both sides.

Length depends on the look you are after

Sill length stops right at the sill and suits kitchens and baths, where fabric near a counter or a tub is better kept short. Apron length runs a few inches past the sill and reads a little more finished. Floor length should end about half an inch above the floor unless you want a deliberate puddle.

• Sill: casual, practical, easy to wash often.
• Apron: covers the frame hardware without sweeping the floor.
• Floor: the full drape, best in bedrooms and living rooms.
• Puddle: add two to four inches past the floor, and accept the dusting.

Fullness is a multiplier, not a match

A panel the exact width of the window hangs flat as a bedsheet. For a gathered look, the fabric across the rod should add up to one and a half to two times the window width. Two 42 inch panels on a 40 inch window is not extravagance, it is the baseline.

Write it on the box

Whatever you measured, write it somewhere that survives the trip to the checkout. The listed size on every design in this catalog is in the spec table on its page, so the comparison is one glance, not a guess in a parking lot.