How does Illustrator calculate the "Fit to page" print option?

Question

I am designing a file that will be printed as A5 (8.5inch x 11inch). I have used these dimensions to create a Z fold publication. So, I have created my design on an Illustrator art board that is also 8.5inch x 11inch.

I have printed out a mock up of the design so far, just to scribble on. I am using a standard A4 printer and A4 paper. The only way of fitting the design was to choose the 'Fit to Page' option on the Illustrator print settings. This is because the Z-fold 8.5inch x 11inch is slightly larger than the size of standard A4 paper.

How does Illustrator calculate what size to resize a design when the 'Fit to Page' option is ticked?

If I was to have an A3 printer printing on A3 paper, and I printed this design and document without the 'Fit to Page' option ticked, would it print the document the correct size, i.e at the 8.5in x 11in Z fold size onto the A3 (11.69in x 16.53in) paper, or would it somehow distort this to fit with the paper?

I've also set a 0.125in bleed around the edge of the document - how does this translate when printing to scale of the document, i.e not choosing the 'Fit to Page' option? If I used paper that was the perfect size of the designed document, I assume this would not be included into the artwork?

Apologies if very silly and unclear questioning. I'm really confused with the whole process and working to create print-ready files, and Googling specific questions leaves me more confused.

Answer 1

"Fit to page" will resize the output to fit the maximum printable area allowed by the printer on that paper. It simply scales it up or down depending on the image:paper size proportion.

If you want to print your document in the correct scale (1:1) you need a larger paper (e.g. letter printed on A3) or your document will be cropped (letter on A4 situation).

Bleed will be printed on the larger paper (because it fits inside the printable area) but maybe not on the smaller (it gets cut off if it's outside of the printable margin) if you're printing on 100% scale.

Answer 2

Two things, Adobe "fit to page" is fitting to print paper dimensions, not the printing dimensions. Printing dimensions are little smaller as there are margins (if you don't override them). Second thing: try not to use metric and imperial sizes. A4 in inches is translated to 209,97x296,93 mm. And although it's a small thing it might bite you later on.

So:

1. when "fit to page" is chosen Illustrator pull the size of the default printer margins and then fit the page inside remaining space. For example in my case the A4 paper is resized to 95,96% to be fully printed. It usually (EU version) resize by the Width of the paper.
2. If you print an A3 file and you would need to choose: A) fit to avaiable paper in printer or B) print as a tile (so file is split by Illustrator into tiles that can be printed on avaiable paper size and then put together for A3) or C) print as is so the only the part that can be printed will the one that can fit on paper (it's the part that is visible in the print preview)
3. Bleed, depending on the chosen output, can be printed (and is then calculated into final page size, so basicaly shrinking if A4+bleed on A4 size) or can be chosen to be ignored. It onyl work if you put bleed in the "Document setup" not when you add it by hand.