IntelliJ how to zoom in / out

Solution 1:

You need to look for the Increase Font Size and Decrease Font Size options on the Keymap menu, you can see the options on my screenshot. You will find the Keymap menu under Preferences > Keymap.

Assigning on those will have the expected effect for font zoom.

Solution 2:

Update: This answer is old. Intellij has since added actions to adjust font size. Check out Wilker's answer for assigning the new actions to keymaps.

Try Ctrl+Mouse Wheel which can be enabled under File > Settings... > Editor > General : Change font size (Zoom) with Ctrl+Mouse Wheel

Solution 3:

Update for intellij idea 2017 3.2