How to Measure for Window Treatments
Measure the window from top to bottom
For a traditional look, measure from 6" above the window frame down to the point where you want the window treatment to hang. You can install the curtain rod lower or higher than 6" above the window, but it should be at least 3 inches above the window. This vertical measurement is the length of the curtains you need to purchase.
Measure the window from side to side
Include the frame in this measurement and add 3" to 6" on each side. This number is the width of your curtain rod and also the horizontal curtain coverage you will need. To achieve standard curtain fullness, multiply this horizontal measurement by two or three. For more fullness and a more dramatic look, you can multiply by three or four, but twice the width of your window is standard. It is customary to have curtains and drapes hang beyond the sides of your window.
Deciding where to hang your curtain rod
Six inches above the window frame is standard. Hanging a rod lower creates a tailored frame appearance, while hanging a rod higher will raise the visual height of the ceiling and create a more dramatic look.