HP Deskjet 5650 - Manual (Page 18)

4. Select a custom paper size name from the Name drop-down list.
5. Enter the paper dimensions in the Width and Length boxes.
The minimum and maximum paper dimensions appear beneath each of the boxes.
6. Select the unit of measurement: Inches or Millimeters .
7. Click Save to save the custom paper size.
You can save up to five custom paper sizes.
8. Click OK to exit the Custom Paper Size dialog box.