Before you can measure your window for curtains, decide where to put the curtain rod. Install curtain rods about 2 to 4 inches above the frame unless you want to create the illusion of a taller window. For a taller look, install the rod halfway between the window frame and the ceiling molding, or 6 to 8 inches above the window trim. Extend the rod at least 3 to 8 inches past the window frame on either side for maximum window exposure. After installing the rod, measure from the top edge of the rod to just a few inches below the window frame, halfway or all the way to the floor for your desired curtain length.
When measuring your windows for curtains, have a little notebook and pen handy to write down the measurements. Add the name of the window to your notes so you remember which window it is when you shop for curtains. Use a steel tape measure and measure to the closest 1/8 inch. Measure each window individually, because even same-size windows might have slightly different measurements due to minor changes and modifications that occur during construction.
Measure the width of the curtain rod bracket to the bracket. For gathered curtains, order curtains that are 1 1/2 to 2 times the width of the curtain rod measurement. To measure for sheers, double or triple that measurement for extra fullness and privacy. Add 12 to 24 inches for lace curtains, unless you want them fuller; then measure 1 1/2 times the rod width. Add 12 inches to the rod measurement for pinch-pleated curtains. To measure for valances and swags, use the measurements as for gathered curtains -- the rod measured bracket to bracket.
Length Measurements by Curtain Type
Choose between rod-pocket curtains, tab-top, pinch-pleated, cafe and tiered curtains or semi-sheers, sheer and lace curtains so that you know how to measure for the curtain type. For curtains, such as pinch-pleated styles that hang from clips or rings, measure from the bottom of the ring to the desired length on the wall 1 to 2 inches below the window frame, all the way to the floor or halfway between the baseboard and window trim. For rod pocket-curtains, including cafe and tiered curtains, and all other curtain types, measure from the top of the rod to the desired length. Cafe and tiered curtains generally only cover the lower half of the window from the rod location to the bottom of the sill or trim.
Measurements for inside-mounted curtains, window blinds or shades represent the exact width of the window opening from one inside edge to the other. Repeat this measurement, using the steel tape measure for the inside height of the window frame. Choose tension rods that fit this measurement and double or even triple that measurement for curtain fullness. Some pull-down shades or window blinds have an adjustable width by about an inch, so select the width that closely matches and verify that it will fit your window. For example, if the inside measurement equals 47 1/2 inches, you may need a blind or shade that measures 47 inches.