https://gist.github.com/vitaLee/5013169
add this to your keybindings
{ "keys": "super+0"], "command": "reset_font_size_to_user_defaults" }
this to your settings
"default_font_size": 10
and create new command in file reset_font_size_commad.py under your user folder
import sublime
import sublime_plugin
class ResetFontSizeToUserDefaultsCommand(sublime_plugin.ApplicationCommand):
    def run(self):
        s = sublime.load_settings("Preferences.sublime-settings")
        if s.has('default_font_size'):
            s.set('font_size', s.get('default_font_size'))
            sublime.save_settings("Preferences.sublime-settings")
that’s it 