custom paper sizes on PRINTING from Photos

Hi - This is one of the ridiculous MacOS behaviours.

You have to first create the custom size in a different app. EG Pages or text edit, from the file>page setup menu. Then you can select it in photos.

Why you can't set a custom size in printer settings that is then available in all apps is beyond me.

You can do as Tony described but you won't be able to print to that custom paper size if your printer does not support it. I've used custom paper sizes, 20" x 30", with Pages to create a collage of photos to be printed by a photo lab.

However, printers can only print to the paper sizes it's designed and programmed form.

Are you really interested in custom paper sizes or custom print sizes? Those are two wholly different situations.