Calculate largest width of a set of elements using jQuery

Here:

var maxWidth = Math.max.apply( null, $( elems ).map( function () {
    return $( this ).outerWidth( true );
}).get() );

Live demo: http://jsfiddle.net/rM4UG/

Fleshing out Marc B's comment, using Math.max():

$(document).ready(function(){
  var maxWidth = 0;
  $('.content ul li').each(function(){
    var itemWidth = $(this).outerWidth(true);
    maxWidth = Math.max(maxWidth, itemWidth)
  });
});