Print on unusual sized paper by creating a custom paper size on Mac
If you want to create a document that has a unique size, such as an envelope or card, first see if the paper size appears in the Paper Size pop-up menu. If not, you can create your own custom paper size.
Note: The following options might not be available for your printer or app. If these instructions differ from what you see onscreen, refer to the documentation that came with the app or printer you’re using.
In an app on your Mac, choose File > Print.
Click the Paper Size pop-up menu, then choose Manage Custom Sizes.
Click the Add button to add a new paper size, then specify the paper size you want.
To print to a custom paper size, choose it from the Paper Size pop-up menu in the Print dialog (choose File > Print). To set a document size to a custom paper size, choose it from the Paper Size pop-up menu.
Tip: If a document is printing with incorrect margins or clipped text, try this: click the Non-Printable Area pop-up menu, choose User Defined, then enter 0 (zero) for the nonprintable margins. In some cases, this allows the document margins to print as expected.