When measuring drapes, measure the window properly, determine window exposure and light blocking, consider room proportions and factor in hardware exposure. Blackout drapes require larger finished measurements than those with regular lining.
Window measurements should run from the outer edge of each side frame and from the apex of the top frame to the bottom of the sill. When measuring for drapes with regular lining, add 15 percent to the window width for full window exposure when the drapes are open, and add 25 percent for blackout drapes.
Individuals who wish to block light on all sides should measure 18 inches past each side and allow room for the drapes to run to the floor. Small windows can appear bigger with large drapes, and adding additional length or width to the fabric helps hide drapery hardware.