I just got a Dell xps 13 with the 1080p screen. Plasma 5 is pretty small in this screen. Is there any way to scale it to about 125-150%? Cinnamon will do 200%, but this is too large.

The UI should follow the (logical) resolution - check "xdpyinfo| grep resolution" - should be ~170dpi for you?

see http://blog.davidedmundson.co.uk/blog/high_dpi_progress

Xdpyinfo shows 96x96. Is this because the Kubuntu live USB I am running on the XPS 13 has Plasma 5.2.2, instead of 5.3.1 like my main Arch box? I chose Kubuntu to try Plasma 5 in a live environment, but I will probably actually install Arch or Antegros.

After doing some fiddling I have found can jack up the font dpi in system settings, which makes things pretty tolerable. The title bar will expand to accommodate larger fonts, and the panel icons expand if you enlarge the panel. A scaling slider in settings would be great though, even if it scaling is also eventually done automatically. This would be great for special cases, such as a media center computer. It would also be an accessibility option for people with limited vision.

Interesting note about xdpyinfo- although it is installed by default in Kubuntu, it's not even in Arch's main repository. And Firefox thinks it should be spelled "informed".

https://www.archlinux.org/packages/extr ... -xdpyinfo/ - all x11 is in extra because it's not required for a system "base"...

try
xrandr --dpi 170
(will afaik only affect new applications)

the detected resolution has nothing to do with kde (unless some local startup script would set it) - it's usually calculated automatically from screen edid and selected mode, but i could imagine that ubuntu has an xorg.conf.d snippet to force it to 96 dpi

the relevant fact is that the oxford dictionary spells it "informed", but i don't see the connection to this topic.

The xrandr line doesn't do anything. Maybe Plasma settings are overriding it? Adjusting the font dpi seems to be a pretty workable solution, though, along with a few other tweaks. Hopefully this is automatic in the future.

Hmmm... the font dpi will be overridden (if you enforced it in "kcmshell5 fonts") and I just checked: at least the breeze GUI style (eg. kwrite GUI) doesn't seem to incorporate the logical dpi (here, maybe there's an updated version) - but eg. fusion (try "kwrite --style fusion", it's a Qt5 built-in style) or virtuality (my style do and soe do the plasmashell QML parts (but you need to restart it)

Also no Qt4 style (but virtuality) seems to incorporate the logical resolution.
Bespin used to check an environment variable, if that helps you anything:

BESPIN_SCALE=1.8 dolphin

Thanks for your help, but I am out of time before my vacation. "BESPIN_SCALE=1.8 dolphin" just starts dolphin with the same ui size. I will try to find time to do a full arch install with Plasma 5 when I return.

The environment variables require you to install and use the bespin, resp. virtuality style.
They have no impact on oxygen, breeze or whatever else.

try "force fonts DPI " to 120