True font size
If I type text in at 12 pt. font size is that the true size that will display on the published book? It appears that my fonts are larger than 12 pt in a page with 2 columns of text in a large format landscape. Also it appears smaller than 12 pt in a 7" square book that I had printed as a test.
I guess I really want to know what is a reasonable size font for readibility with a lot of text? I have seen mention of 9 pt fonts, but that seems very small to read. Maybe its my over 40 year old eyes that are the problem.
I’ve made both 13" x 11" and 10" x 8" books and I hadn’t spotted a difference in the printed size of text for a given font size, maybe I should take a ruler to those? So I’m not sure whether 11pt really printed as 11pt.
I use 9pt non-seraph fonts for my captions, mainly because the caption text boxes are fairly small and I’m obvioulsy a bit verbose. I find non-seraph’d fonts to be easier to read at that size.
But I found that large bodies of text that size a bit of a strain. So I now use 11pt (seraph or non-seraph) fonts for those and have no problems (with my 60+ eyes). I tried 13pt but found that just looked too large for bodies of text, but I use that size for sub-headings. I think your 12pt should be fine.
Further to Tony, I think font size to use depends a bit on (i) the particular typeface, (ii) whether you’re putting text straight into a BookSmart text box (sharp) or bringing it in as part of a bleed page.
I used a spindly font so made it a little larger at 12 point. Sharp and easy to read black on white and white on black. Though I haven’t measured, it looks very close to 12pt printed.
With patience you can see in online Preview, though not exact size. Once loaded, use right-click zoom enlarge once or twice to see clearly: