This tool is a quick reference for viewing a website in a few popular devices. It does not qualify as an absolute guarantee the site will be exactly as portrayed here, though this is a good guideline.
Hover over each dimension button to identify the corresponding device(s).
Disclaimer: This is a simple tool. In practice, I normally use Chrome's (View -> Developer -> Developer Tools) and FireFox's (Tools -> Web Developer -> Responsive Design Mode) developer tools.
A good reverence for viewport sizes is this site or this site .
 For example, Retina displays are not represented in this demo.