By default, elementary OS only has an option in the System Settings panel (System Settings > Universal Access > Seeing:Display > Reading > Text Size) to globally alter the font scaling. I am fine with the fonts at the normal setting, but monospaced fonts on dark backgrounds are to difficult to see at 10px (default) so I need to set it to 11px.
- Go to the AppCenter and search for dconf. The dconf Editor should pop up. Install it.
Open dconf Editor and navigate to org > gnome > desktop > interface
Scroll down until you find monospace-font-name
Change Roboto Mono 10 to a monospace font of your choosing, followed by the size. In my case I used Hack 11. (Check your Font Viewer to see what fonts you have available)
- Look for other system fonts you’d like to adjust, and tune to your liking.
Keep in mind that there are some fairly advanced settings in there so be sure to tread lightly.