Print on special and custom-size paper
If your application supports custom-size paper, set the size in the application before
printing the document. If not, set the size in the printer driver. You might need to
reformat existing documents to print them correctly on custom-size paper.
Use only custom-size paper that is supported by the printer. For more information, see
NOTE: Defining custom-size media sizes is only available in the HP printing
software in Mac OS X.
Follow the instructions for your operating system.
Print on special or custom-size paper (Mac OS X)
Set up custom sizes (Mac OS X)