Determining Correct Display Resolution

I have been banging my head against this problem for a while and am hoping that somebody can help me, or at least explain why it is not possible.

I am doing some layout for a book on my iMac (Retina 4K, 21.5-inch, 2017) and would like to see pages at actual size, by which I mean that if the font size is 12pt, the bounding box is in which letters are framed is 1/6th inch (or 12 * 0.353 = 4.24mm) when the application’s zoom is set to 100%.

My iMac’s display resolution is set to “default for display”, but I’m flummoxed as to which (if any) of the alternative resolutions achieves what I’m looking to do. By preference I’d like away to do this only for windows containing printed text, I don’t really want the menu bars and other controls to scale widely even though I’m expecting I’ll have to suffer that.

Alternatively, how do I work out what zoom to set an application at to achieve the desired effect?

As an aside, this seems a prevalent issue/ bug. For example, I have Mail’s font set to Helvetica 12pt, but it’s almost too small for me to read at a comfortable viewing distance (ageing eyes) .


I appreciate that there are different definitions of the printer’s point (Didot, Fournier etc.), but I’m happy to go with the Postscript value of 1pt = 0.353mm or as near as makes no difference 1/72in.

I also appreciate that a standard A4 page at this scale will not fit vertically on my screen, that’s OK; it’s what an application’s zoom feature is for!