How to change font size in emacs?
Solution 1:
The temporary solution
You can press C-x C-+ and C-x C-- to increase or decrease the buffer text size.
The permanent solution
Put the following in your .emacs-file:
(set-face-attribute 'default nil :height 100)
The value is in 1/10pt, so 100 will give you 10pt, etc.
Source: How to set the font size in emacs?
Solution 2:
A slightly different way to do the same thing, by setting botht the font and size in one go, again in the .emacs file. If you want to use a differing font check it exists first or you will get an error message.
(set-default-font "Monospace-12")