So, you can do this:

"Device mode" button in Chrome's developer tools(/images/device-emulation-in-chrome.png)#

This is in Chrome's "Developer Tools" console, which you can bring up with ctrl-shift-I or by hitting Chrome's menu and selecting More Tools | Developer Tools.

When you hit that button, Chrome pretends to be a handheld device (and you can set the screen dimensions yourself, if you need to), so you can see how your web site will look on that device.