Window blinds and shades are a popular solution for covering windows and patio doors. If you have a sliding glass patio door, you need to measure carefully and consider the type of shade or blind you are installing in order to come up with the correct measurements.
Determine the type of shades or blinds you will be installing. Vertical blinds are a common solution for sliding glass doors because they can be opened to one side, exposing the door part while covering the rest of the window. You can also use pleated shades, honeycomb shades or roller shades. If you decide to get a type of shade that goes up and down, you need to decide if you want one large shade or two side-by-side shades that can work independently so you can uncover the door while leaving the other side of the window covered.
Decide between an inside mount and and outside mount. Vertical blinds will be an outside mount, meaning the head rail is mounted to the wall above the window opening. Shades are typically an inside mount, installed inside the top of the window frame so the shade covers the width of the window only and doesn't overlap with the wall at all. Shades can have an outside mount if you have a special reason for doing so, such as a window frame that doesn't allow space for an inside mount, or a desire to hide the window frame or make the window look larger than it really is. Another thing to consider with a sliding glass door is whether the door handle sticks out too far to make an inside mount practical.
Measure the width of the window. For an inside mount, measure the exact width from the inside edge of the frame on the left to the inside edge of the frame on the right. Measure at the top and bottom of the window, and again in the middle. Write down the narrowest width of the three, and use that, rounding down to the nearest 1/8 inch. For an outside mount, measure to where you want the edges of the shade or blind to cover on either side of the window. Typically, vertical blinds extend 4 or 5 inches beyond the the actual window, while shades with an outside mount usually cover 1-1/2 to 2inches of the wall on either side of the window. Take the width of the window trim into consideration when measuring for outside mount blinds and shades.
Measure the height of the window. For an inside mount, measure the exact height from the inside of the top of the window's trim at the top to the inside of the trim on the bottom (or the floor). Measure in on the left, on the right and in the center, and take the tallest measurement, rounding up to the nearest 1/8 inch. For outside mount shades, measure from where you want the top of the head rail to go, at the top, down to the floor. Height is extremely important with vertical blinds, and not as specific with shades that go up and down because you can always let the shade down almost all the way and the window will be covered. Any extra will not be very noticeable.
Double-check your measurements. Be sure that you have written the width first, and then the height, and not the other way around.
Specify where the cord will go. You don't want the cord to hang on the side of the door where the door opens. Since sliding doors can go either way, you need to specify where to put the cord and, for vertical blinds, the wand that is used to pivot the vanes. For vertical blinds, you want to specify left or right stack, meaning that the vanes, when open, will all go to one or the other side (same side as the cord, opposite side from where the door opens) rather than opening from the middle as they generally do with a regular window.
Pay special attention if you are specifying two side-by-side shades. Measure each side separately to see if both sides of the window are the same width. Consider the width of the frame around the movable part of the door to ensure there is not a gap in the middle where light will show through.