Things You'll Need
Screen doors are almost always adjustable to a few inches. The rollers can move up and down so the door can fit into a few different openings.
Sliding screen doors are found on most patio doors. They are attached to a track above and door and along the threshold below. These screens are convenient because they allow the patio door to be open. Air can then come into the house without allowing insects to enter. There are different types of screen doors depending on the manufacturer of the patio door, but for a generic screen, measurements can be taken so the proper size screen can be installed.
Unlock and slide open the patio door. Locate the header at the top of the track on the inside of the patio door. Feel the shape of the track at the top and determine if it is T-shaped or U-shaped.
Measure from the top of the track at one end of the door down to the threshold on the ground with a tape measure. Write down the measurement. Move halfway down the opening and measure again. Write down the measurement.
Measure a final time from the end of the door. Compare the measurements and make sure they all match up. This will verify the door is square and plumb in the opening.
Add 3/8-inch to the measurement for a T-shaped header and 1/8-inch for a U-shaped header.
Alexander Callos began writing in 2005 for "The Lantern" at The Ohio State University and has written for various websites, including Bleacher Report, Top Ten Real Estate Deals and Columbus Sports. He has published articles for CBS Sports, SI.com and other websites. He graduated in 2007 from The Ohio State University with a bachelor's degree in public affairs journalism.