Create a custom page size.

Way described below is alternative and to be used only in exceptional cases.
Follow this link to find out how to create a custom page size default way:
ImagePrinter Pro – Basics

1. Windows XP. Windows 2003

Start the Printer control applet (Start – Settings – Printer)
From the File menu select “Server Properties” (Print server properties)
Forms tab – Click “Create a New Form” and add information that you want
Click OK

2. Windows 7 and Later

Start the Control Panel -> System and Security -> Administrative Tools
Open Print Management
Open – computer name
Click on Action menu > Manage Forms…

Click Create a new form
Define width and height

Click OK