Choose a window shade to determine the depth of the blind, which will be provided by the manufacturer. Different blinds have varying depths and will make a difference how the blinds hangs on the bay window.
Figure out the intersecting points of each separate window to calculate the width of each blind.
Cut two pieces of cardboard similar to the thickness of the window blinds and about 12 inches long. Place the cardboard so the front edges slightly touch at the meeting points like the blinds would. Draw a line with a pen on the edge of the cardboard where the pieces meet. Repeat this step for each intersecting point.
Measure each bay window blind. The left window blind measurement is the meeting point marked on the window frame. The measurement should be the same distance from the left side of the window as the intersecting point. Repeat this method for the right blinds, and use the intersecting point on that side. Figure out the measurements for the center window by measuring the distance from the left and right intersecting point.
Add 2 inches to the height to account for brackets. Measure the exact width of the windows for inside mounts. Outside-mounted blinds should rest just outside the window frame. Convert measurements to the nearest 1/8 inch.
- Since bay windows are three windows positioned on an angle next to each other, it will be difficult to avoid gaps between the blinds. Take accurate measurements to limit these spaces.