Ethan Marcotte’s excellent Responsive Web Design (published in 2011 and that will matter as time goes by) has a handy table of device-width breakpoints for building a Website that responds to the visitor’s context. I find it so handy that I’m putting it here, without apology, for easy reference. Really, though, you should buy the book.
|320 pixels||For small screen devices, like phones, held in portrait mode.|
|480 pixels||For small screen devices, like phones, held in landscape mode.|
|600 pixels||Smaller tablets, like the Amazon Kindle (600×800) and Barnes and Noble Nook (600×1024, held in portrait mode.|
|768 pixels||Ten-inch tablets like the iPad (768×1024) held in portrait mode.|
|1024 pixels||Tablets like the iPad (1024×768) held in landscape mode, as well as certain laptop, netbook, and desktop displays.|
|1200 pixels||For widescreen displays, primarily laptop and desktop computers.|
Personally, I rarely find much reason to make a site wider than 1000 pixels and often restrict the width using
max-width. But that could just be me.