An A9 page is 37 x 52 mm. The sheet is A3, 297 x 420 mm, a built-in preset in FitPrint. The layout below is what FitPrint produces with its defaults: Fit most packing, Original size scaling, a 5 mm gap between items and a 5 mm side margin. Nothing is scaled: each item is placed at 37 x 52 mm, its true size.

Where each item lands

Positions are millimetres on the A3 sheet as FitPrint wrote them, with y measured from the bottom edge.

x (mm)	y from bottom (mm)	Width (mm)	Height (mm)
10.71	361	37	52
58.43	361	37	52
106.14	361	37	52
153.86	361	37	52
201.57	361	37	52
249.29	361	37	52
10.71	302	37	52
58.43	302	37	52
106.14	302	37	52
153.86	302	37	52
201.57	302	37	52
249.29	302	37	52
10.71	243	37	52
58.43	243	37	52
106.14	243	37	52
153.86	243	37	52
201.57	243	37	52
249.29	243	37	52
10.71	184	37	52
58.43	184	37	52
106.14	184	37	52
153.86	184	37	52
201.57	184	37	52
249.29	184	37	52
10.71	125	37	52
58.43	125	37	52
106.14	125	37	52
153.86	125	37	52
201.57	125	37	52
249.29	125	37	52
10.71	66	37	52
58.43	66	37	52
106.14	66	37	52
153.86	66	37	52
201.57	66	37	52
249.29	66	37	52
10.71	7	37	52
58.43	7	37	52
106.14	7	37	52
153.86	7	37	52
201.57	7	37	52
249.29	7	37	52

What other settings place

Settings	Items per sheet	Placed size
Fit most, 5 mm gap and 5 mm margin (default)	42	37 x 52 mm
Stack, 5 mm gap and 5 mm margin	7	37 x 52 mm
Fit most, no gap or margin	64	37 x 52 mm
Fit most, 10 mm gap and 10 mm margin	36	37 x 52 mm
Stack, no gap or margin	8	37 x 52 mm

Turned landscape, 55 fit: A9 pages (landscape) on A3 (fit most, no gap or margin).

What the status line says

With 42 A9 pages in the list, FitPrint's status line reads exactly "42 items · 1 A3 sheet". Add one more and it reads "43 items · 2 A3 sheets": the extra item starts a new sheet rather than shrinking anything.

How to lay this out in FitPrint

Drag your files in. Open FitPrint and drag your A9 page files onto the window. Each file appears in the list with its size in the caption.
Choose the A3 sheet. Click A3 in the sheet preset grid. FitPrint then lays the items out on a 297 x 420 mm sheet.
Keep scaling on Original size. Original size places every item at 100 percent, so a printed item measures exactly what the file says it measures.
Leave packing on Fit most. Fit most packs as many items per sheet as fit. With the default 5 mm gap and 5 mm side margin that is 42 A9 pages per A3 sheet.
Change the gap or side margin only if you need to. The defaults are a 5 mm gap and a 5 mm side margin. The settings table on this page shows what every other recorded setting places on this sheet.
Export and print at actual size. Click Export PDF, then set Scale to 100 percent and Pages per Sheet to 1 in the print dialog so nothing re-scales the exported file.

42 A9 pages fit on one A3 sheet at actual size

Where each item lands

What other settings place

What the status line says

How to lay this out in FitPrint

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