Core Add-in, Google Analytics Connector
This free report presents the Google Analytics screen resolution (or the new browser size) dimension the way it should be — showing the percentage of website users served by various combinations of screen widths and heights.
The report auto-adjusts to your site data, showing the most common size increments that your website visitors use.
The two-axis table and conditional formatting make it really easy to zero in on the target screen sizes that a specific percentage of users have. For example, in the sample image, 81% of visitors have screens 1280 wide x 768 high.