Size of the resulting sheet can be calculated automatically depending on the number and size of positions, gaps and margins, or it can be selected manually either from pre-set common formats or by making a new one. To make a new format you need to set its height and width (these two sizes can be switched by pressing the portrait and landscape buttons). Custom formats can be saved under custom names (floppy disc icon), edited (pen/paper icon) or deleted (trash icon). If a star is displayed next to the name of a format it indicates that it was selected, but its height/width was changed.
Minimal sheet size necessary for all positions including margins is also displayed on the palette if automatic calculation is disabled.
The Edit button can be used to get an overview of all preset and custom formats and to edit them. The 'Read only' attribute can be set and disabled for formats here to avoid unintentional changes and the non-printable area of the sheet (only visible in preview, not affecting the imposition itself) can also be set here.
Sheet size cannot be calculated automatically if the 'Calculate automatically' feature (for rows and columns amount) on the Imposition appearance palette is enabled.