Track actual browser width (not screen resolution) in Google Analytics.

gistfile1.txt

/**
 * Creates a Google Analytics Event on page load that tracks which default
 * Bootstrap screen width category the user's browser falls into.
 *
 * See http://getbootstrap.com/css/#grid-media-queries
 */
var width  = window.innerWidth  || document.body.clientWidth;
var bootstrapSize  = 'Extra Small (xs)';
if (width >= 768) {
  bootstrapSize = 'Small (sm)';
}
if (width >= 992) {
  bootstrapSize = 'Medium (md)';
}
if (width >= 1200) {
  bootstrapSize = 'Large (lg)';
}
_gaq.push(['_trackEvent', 'Bootstrap Browser Size', 'Page Requested', bootstrapSize]);