After a long search, I’ve used the Expert configuration dialogue to set the default font for Calc to “Segoe UI” (org.openoffice.VCL.LocalizedDefaultFonts[‘en’] / LATIN_SPREADSHEET), without using templates. However, citing my age, 61, it would be nice if there was a setting to change de default font size from 10 to 12, but doing a search for “10” doesn’t (seem to) give any meaningful results, unless I’m overlooking them.
Can anyone give me a clue?
Segoe UI is a bad choice of default font. It is a Microsoft brand font and is not to be used on on non-Windows apps so your documents won’t look the same and will have to use a substitute font for anyone using a different operating system.
See, about 3/4 way down, Font redistribution FAQ - Typography | Microsoft Docs
Liberation Sans is default because it has similar metrics to Arial and to Helvetica so font substitutions are barely noticeable for length. There are a vast number of freely licensed fonts on Internet, a search in Google Fonts should bring a good selection.
I though FOSS was about choice? My choice happens to be Segoe UI.
Microsoft is not FOSS. You have chosen to use a proprietary font that is not licensed for use outside Windows (non-FOSS)
I like 9 pt Verdana for the default in Calc. I modified the default cell style, saved as a template, made the template the default template. This means I always get the settings I want without having to mess with Expert Configuration. LibreOffice remembers this when updating to new versions. P.S. I use Andika from sil.org for everything else and share docs as PDF.
It would have been better to ask first and then act. The expert configuration is not advisable for your case.
You can set the font and font size via the Tools menu, see Basic Fonts Western.
…citing my age, 61…
Ah, if I were still so young. 
Basic Fonts Western is for Writer. I need a default font size for Calc, and like what I did for the default font, I would like it to be there is I open a new spreadsheet, without having to fiddle with templates and the like.
I need a default font size for Calc,…
Yes, sorry I overlooked the tag “Calc”.
But then the best solution is to create a blank document with the desired font and font size and then save it as a document template “Default” (default template).
To be honest, I don’t understand when someone wants to do without a clear solution such as a standard document template because it supposedly seems too difficult, but is fumbling around in the expert settings.
I’m out of here, out of this thread, by.