Setting tab size in Emacs

I'm using Emacs as an editor. I want to set the tab size to four spaces. In my .emacs file I have the following:

(setq default-tab-width 4)

I've also tried:

(set-default tab-width 4)

Either way, when I open emacs and try to tab, it inserts two spaces. Am I doing something wrong? It almost seems like its not seeing my .emacs file.

Any suggestions would be great! Thanks!