title_body: Choosing the right dimensions for ePub
upvoted_answer: First, you are way behind the current standard. 
  
  Most (if not all)  ebook distributors are requiring high resolution graphics for cover images. (a Minimum of 1500 pix or 2000 pix for width). This has been true for at least the last 2 years. 
  
  It's true that some of the smaller devices will display only 600x800, but all distributors recognized early on that it's easier to require a high resolution cover graphic and then downconvert rather than accept smaller graphics which can't be converted to the newer screens. 
  
  Second, I'm assuming you are not using Indesign for a Fixed Layout. Fixed layout requires you to set dimensions etc, but this is NOT epub. Epub is more flexible for a variety of standards. That indeed is the point. 
  
  Amazon (which doesn't accept epub but lets you convert from epub to a Kindle format) has a tool called Kindle Previewer which also lets you emulate the various Amazon devices. http://www.amazon.com/gp/feature.html/ref=amb_link_359603222_5?ie=UTF8&amp;docId=1000765261
  
  I found that on Chrome there is an extension called "Screen Resolution Tester" which lets you simulate various display sizes https://chrome.google.com/webstore/detail/screen-resolution-tester/bnbpeddmakpmblddofjnoghpjminhjph?hl=en
  
  You can also check this reference guide for screen sizes. http://mydevice.io/devices/
  
  This should get you started. I would start by testing dimensions for oldest Amazon Kindle Fire, ipad 1 or 2, ipad 3, the 7 inch ipad, iphone, Galaxy Tab 7 and 10.