Since a search for this does not result in any hits on the apple.com web site (for instance not “To create a new paper size based on an existing size, select a paper size in the list, then click Duplicate.”), I have quoted it in full.
The main reason: “to change the name, double-click, then type a new name”
I needed this to specify A0 size, in inches, which was hard to find exact dimensions with more than 1 decimal digit, but luckily- unlike ISO 216 – Wikipedia:
- [WayBack] The A0 paper size | dimensions, usage & alternatives DIN A0 measures 841 × 1189 millimeters or 33.11 × 46.81 inches. In PostScript, its dimensions are rounded off to 2384 × 3370 points.
- [WayBack] The A1 paper size | dimensions, usage & alternatives: DIN A1 measures 594 × 841 millimeters or 23.39 × 33.11 inch. In PostScript, its dimensions are rounded off to 1684 × 2384 points.
- [WayBack] The A2 paper size | dimensions, usage & alternatives: DIN A2 measures 420 × 594 millimeters or 16.54 × 23.39 inches. In PostScript, its dimensions are rounded off to 1190 × 1684 points.
- [WayBack] The A3 paper size | dimensions, usage & alternatives: DIN A3 measures 297 × 420 millimeters or 11.69 × 16.54 inches. In PostScript, its dimensions are rounded off to 842 × 1190 points.
- [WayBack] The A4 paper size | dimensions, usage & alternatives: DIN A4 measures 210 × 297 millimeters or 8.27 × 11.69 inches. In PostScript, its dimensions are rounded off to 595 × 842 points. Folded twice, an A4 sheet fits in a C6 size envelope (114 × 162 mm).
- [WayBack] The A5 paper size | dimensions, usage & alternatives: DIN A5 measures 148 × 210 millimeters or 5.83 × 8.27 inches. In PostScript, its dimensions are rounded off to 420 × 595 points.
- [WayBack] The A6 paper size | dimensions, usage & alternatives: DIN A6 measures 105 × 148 millimeters or 4.13 × 5.83 inches. In PostScript, its dimensions are rounded off to 298 × 420 points. The matching envelope format is C6 (114 × 162 mm).
- [WayBack] The A7 paper size | dimensions, usage & alternatives: DIN A7 measures 74 × 105 millimeters or 2.91 × 4.13 inches. In PostScript, its dimensions are rounded off to 209 × 298 points.
- [WayBack] The A8 paper size | dimensions, usage & alternatives: DIN A8 measures 52 × 74 millimeters or 2.05 × 2.91 inches.
And there is the millimeter specs (and way more) at [WayBack] A4 paper format / International standard paper sizes.
The quote from [WayBack/Archive.is] Create a custom paper size for printing on Mac – Apple Support:
Create a custom paper size
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. Custom paper sizes aren’t available for some printers or for all apps.
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 you’re using.
- Choose File > Print. If you see a Show Details button, click it to show all available options.
- 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 create a new paper size based on an existing size, select a paper size in the list, then click Duplicate.
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 in the Page Setup dialog (choose File > Page Setup).
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 zero for the nonprintable margins. In some cases this allows the document margins to print as expected.
–jeroen