title: OS X icons size
body: <p>What size should an application icon and menu bar icon for OS X be?  </p>
  
  <p>I can deal with small resolution displays but what about Retina - does an icon displayed on the menu bar (e.g. 20 x 20 ) will be smaller or blurred on a new MacBook Pro with Retina display? 
  I reckon that the Application icon will be scaled, so if I'll prepare twice larger than regular it should be OK on Retina.</p>
  
  <p>I found an excellent guide for iOS development with sizes specification but I can't find similar size specifications for OS X. </p>