Visual Studio 2013 editor default font size?

[Tools] -> [Options] -> [Environment] -> [Fonts and Colors]

THEN

Select from "Show settings for:" drop-down list.

THEN

Change font size in "Size:" text field.

LEGEND:

[...] = Button/Click

"..." = Label

Press Tools -> Environment -> Fonts and Colors -> Show Settings for: Text Editor there ist the Font Size Property.

Note that: The settings for Font and Size are global for all text elements in all Visual Studio editors. According to How to: Change Fonts and Colors in the Editor