How to change MuseScore's DPI

An unsolved bug sometimes leads MuseScore to mistake your monitor's settings, and display items as too small or too large.

To fix this, you can launch MuseScore from the command line with the -D option followed by the correct DPI value (needs MuseScore 2.1 or later), at which point MuseScore should open with the display scaled correctly. Launching from the command line on a regular basis is inconvenient; however, it is possible to set it up to use your chosen DPI option automatically.

Figure out your DPI

If you don't know your DPI yet, you can either "do the math" (screen width / height / diameter, Pythagoras: w² + h² = d²) or try out some values by experiment until you find one that works for you.
Common values are: 72, 92, 96, 100, 120, 150, 200, 224, 240, 300

Windows

Open the windows command prompt and type your desired dpi as an argument. With the default installation path the command for a dpi of 150 should look like this:
"C:\Program Files\MuseScore 3\bin\MuseScore3.exe" -D 150

See this screen capture showing the result of testing out some values:

Make it permanent

1. Right-click the program icon and choose Properties...
2. A dialog will appear allowing you to customize the command line option that is used to start the program.

Mac

1. Open the Automator app and choose "Application" (the second option) at startup.
2. On the left of the window, scroll down or search for "Run Shell Script."
3. When you find it, drag and drop it into the right half of the window.
4. Replace "cat" with the path to mscore (probably /Applications/MuseScore\ 2.app/Contents/MacOS/mscore or /Applications/MuseScore\ 3.app/Contents/MacOS/mscore), followed by the correct DPI argument (e.g., -D 102), followed by &.
5. Save the application and going forward open it instead of MuseScore.