Changing the code font size in WebStorm IDE

Solution 1:

Settings (Preferences on Mac) | Editor | Colors & Fonts | Font, Size:

Before you can change this setting you must click "Save As..." and save the scheme under a custom name.

Solution 2:

If you came here because you already found that screen, but the text box was locked...

This is because you cannot modify the current theme.

Click "Save As..." to save a copy of your current theme, now you should be able to edit whatever you want.

Solution 3:

There is also an option to enable mouse wheel zooming, like in browsers:

File > Settings > Editor > Change font size with Ctrl+Mouse Wheel.