How many fit on a sheet.
Pick a piece and a press sheet — the layout draws itself, both orientations tried.
8 up — 2 × 4 A6 pieces, turned sideways, on SRA3, using 86% of the sheet · the other orientation manages 4.
Straight guillotine layout — both orientations tried, best shown. Margin is kept on all four edges; the gutter separates pieces. Mixed-orientation nesting can sometimes squeeze in more; ask your printer.
Planning artwork instead? Every size's pixel dimensions at print resolutions live on its own page.