Epson CX6500 Reference Manual page 143

Type a unique name for the paper size in the Paper Size
list.
Choose either cm or inch as the Unit
setting.
Enter the width and the height of your paper by typing the values in the appropriate text
boxes.
Note:
Although you can define a large range of paper sizes, the size of paper you can feed into
the CX6500 is limited by the size of the sheet feeder on your CX6500. Therefore, if
necessary, it is recommended that you reduce or enlarge documents to fit paper sizes
within the range of your CX6500's capabilities.
Specify the margins by typing in the Margin text boxes or by manipulating the margins in the
preview image.
Click OK to return to the Page Setup dialog
box.