Create Custom Page Sizes
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 12 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.