Create Custom Page Sizes in Photoshop Elements
Locate the Default New Doc Size file and copy the existing page size.
On both Windows and the Mac, the Default New Doc Sizes text file is available in the same location. Open your Photoshop Elements folder. Open the Locals folder and then open the Settings folder. Inside this folder, you find the Default New Doc Sizes file.
Make a copy of the file and place the copy on your desktop.
Open the Default New Doc Sizes file in a text editor (WordPad, NotePad, or TextEdit) and select the Letter line. Be certain to select the entire line. Press Ctrl/Command+C to copy the text.
Paste the text on a new line. Rename it and change the sizes.
Add a carriage return to the line you copied and press Ctrl/Command+V to paste the text.
Give the line a new name, such as Letter Landscape. Change the size values, such as from the default sizes of 8.5 and 11 to 11 and 8.5 for a landscape orientation.
Rename the original file in the Settings folder to keep a copy of it and drag it to your desktop. Drag your edited text file to the Settings folder and launch the Photo Editor.