It's as simple as Ctrl + mouse wheel. If this doesn't work for you, enable File → Settings → Editor → General → (checked) Change font size (Zoom) with Ctrl+Mouse Wheel.

It is possible to change font size etc when creating custom Scheme using Save As... button:

To change font size using the keyboard

In Windows or Linux press Ctrl+Shift+A

In MAC press CMD+Shift+A

In the popup frame, type Increase font size or Decrease font size, and then click Enter.

Font grows larger or smaller.

To change the font size in the current version of IntelliJ IDEA, go to File → Settings → Editor → General. In the dialog box, and check the item labeled "Change font size (Zoom) with Ctrl+Mouse Wheel".

In IntellJ 13

File 
 |
  ---- Settings 
       |
        ------- Editor
                 |
                  ------- Colors & Fonts
                          |
                           ------ Font -> [Size]

For Intellij 2018 it's quite confusing as there's an Editor → Font section but it's usually overriden by Editor → Color Scheme → Color Scheme Font:

On a Mac you can also pinch-zoom, i.e. move your thumb and index finger together or apart.

On Mac: IntelliJ Idea → Preferences

In the Preferences Dialog,

1. Editor → Colors & Fonts → Font.
2. Click on Save As, enter the scheme name such as the mac user name.
3. Change the Size as required.

On Mac Os, go to Preferences > Editor > Font > Size . Enter the new font size.

More details read this blog post

Curious how it's done on Linux and Windows

As of InteliJ IDEA 2017.2.5, you can change the editor font size by going to:

Settings ▶ Editor ▶ Font

First press Ctrl+Shift+A

then search increase font

For Mac Users, It's cmd + shift + A

The font used in menus, dialogs and tool windows can be changed in Settings > Appearance & Behavior > Use custom font.

It's not possible. Please, vote for the bug.

Shortcut is Ctrl+Shift+A - Then Type Increase font size then Enter

There are two places where you can change the appearance:

1. File -> Settings -> Appearance & Behavior -> Appearance -> Use custom font -> Size

GUI size

2. File -> Settings -> Editor -> Font -> Size

Editor Font

The first controls the font size of IntelliJ GUI (menus etc). The second one is for the editor.

You can use Presentation Mode to temporarily increase the font size.

Note: The location of this menu has changed. It's nearer the top.

Enable Presentation Mode with View -> Enter Presentation Mode

I needed to increase the default font size for presentation mode. To do this, open Settings and typed "presentation mode" in the search bar. Under appearance, scroll down to Presentation Mode, and select your preferred font size.

Because I use it frequently, I mapped "toggle presentation mode" to Ctrl-P. Under "Keymap", right-click on "Toggle Presentation mode" and select "Add keyboard shortcut"

Literally press the Control and P keys and then hit OK to enable this.

For newest version of IntelliJ, i think option has changed a bit.

Screenshot:

My current version of IntelliJ:

IntelliJ IDEA 2017.3.5 (Community Edition)
Build #IC-173.4674.33, built on March 6, 2018
JRE: 1.8.0_152-release-1024-b15 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o

Hope this will help.

On Intellij Idea 3.3(Ultimate) System : Mac

IntelliJ Idea → Preferences (CMD + ,) → Editor → General(Main) : Uncheck/Check "Change font size(Zoon) with Command + Mouse Wheel"

CTRL+SHIFT+A type increase and press Enter, repeat by just pressing again CTRL+SHIFT+A and then Enter until you are satisfied

If you need to do it often than add a custom shortcut to it :

Alt + Num pad + and Alt + Num pad - are free

If you don't want to change keymaps you can quickly enter and exit Presentation Mode via the following shortcut sequence (use Ctrl in macOS, too):

1. Ctrl+` (Switch...)
2. 4 (View Mode)
3. 1 (Enter/Exit Presentation Mode)

Goto->Settings->Editor->Fonts->Schemes option. Then rename that options and apply, then choose the new option (renamed one) then option to edit font size will be enable.

Change the "Color Scheme Font". and you will get what you want. I have faced the same issue and fixed it.

So there are several ways you can do it:

1. Windows or Linux press Ctrl+Shift+A
   In the popup frame, type Increase font size or Decrease font size, and then click Enter

2. go to File → Settings → Editor → General. In the dialog box, and check the item labeled "Change font size (Zoom) with Ctrl+Mouse Wheel"

3. go to File → Settings → Editor → Font. Change the font size and click OK/Apply button.

In 2021-12, Pycharm 2021.3 (Professional Edition) and probably community edition as well, you can activate the ability to zoom in and out on the current or all files by:

File > Settings > Editor > General > Mouse Control

and checking off

Change font size with Ctrl + Mouse Wheel In