How to Determine Window Curtain Length & Width
Measuring for window curtain length and width depends on what kind of curtains you want. Do you want them to cover the window frame entirely and reach the floor? Or do you want cafe style curtains that only cover the window and hit the bottom of the pane? You can also select curtains that mount inside the frame to expose any decorative mountings. Decide what kind of coverage you want from the curtains before you start measuring.
Interior Frame Mounting
Measure the width of the frame from one side of the window to the other. Make the first measurement at the top of the frame. Round to the nearest 1/8 inch.
Measure the width of the frame in the middle of the window and at the bottom. Take the narrowest measurement as the measurement for your curtain.
Measure the height of the window from the inside of the top of the frame to the inside of the bottom of the frame. Make the first measurement on the right side of the window, and round to the nearest 1/8 inch.
Measure the height of the window in the middle of the frame, and then on the left side. The longest measurement will be the length of the curtain.
Mounting Outside the Frame
Measure the width of the window at the top of the frame, measuring from the outside edge of the molding to the other outside edge. Round to the nearest 1/8 inch.
Measure the width again at the middle of the frame and the bottom of the frame. The widest measurement will be the width of the curtain. Add 8 inches to the measurement if you want the view out the window to be totally unobstructed when you open the curtains.
Measure the height of the window from the top of the frame to the floor, for floor length curtains, or from the top of the frame to the bottom frame, for cafe style curtains. Add 2 inches to the measurement to account for the height of the curtain rod brackets.