Switching the Sony Xperia XZ Premium phone to 4K

With the usual (factory) settings, the XZ Premium phone only uses a quarter of the native resolution most of the time. Only specific applications take advantage of the 4K resolution. However, it is possible to switch the phone to 4K entirely and permanently. These instructions describe how to do this using an ADB connection over USB from a computer.

On a Windows computer, you need to have ADB, a tool of the Android SDK, installed with the path to the tool set in the Windows system environment. The Android SDK is present for example after installing Android Studio.

1. On the phone:
   Become a developer:
   Go to Settings → System → About phone, and tap Build number 7 times
2. On the phone:
   Go to Settings → System → Developer options, and turn USB debugging ON
3. Connect the phone to the computer over the USB cable.
   A dialogue will pop up on the phone screen: Allow access? .... Tap on ALLOW.
4. On the computer:
   Windows: Launch a terminal window using Start → Run (right mouse button hovering over Start Icon), and open cmd
   Linux: Launch a terminal window and log in as root
5. On the computer:
   Type adb shell on the command line, press enter
6. On the phone:
   A dialogue will pop up: Allow USB debugging? .... Tap on OK
7. On the computer:
   Type wm size 2160x3840 on the command line, press enter
   (the change should be visible immediately on the phone screen)
8. On the computer:
   Type wm density 820 on the command line, press enter
   (the change should be visible immediately on the phone screen)

You are done - enjoy the full resolution!

To switch the phone back to FullHD, use wm size 1080x1920 and wm density 410