$(function(){
var target_width = $('.target').width(); // get target width
$('.target2').width( target_width ); // set target width
$('.target2 .width2 span').text( target_width );
$('.width_log span').text( $('.target').width() );
$('.innerWidth_log span').text( $('.target').innerWidth() );
$('.outerWidth_log span').text( $('.target').outerWidth() );
$('.windowWidth_log span').text( $(window).width() ); // returns width of browser viewport
$('.documentWidth_log span').text( $(document).width() ); // returns width of HTML document
});
<div class="well target">
<span class="label label-warning">.target</span>
<p>set in css:
<span class="label label-info">width: 400px;</span>
<span class="label label-info">padding: 10px;</span>
<span class="label label-info">margin: 12px;</span>
<span class="label label-info">border: 2px;</span>
</p>
</div>
<div class="well">
<p>get .target properties with jQuery:
<span class="label label-success width_log">
.target width: <span></span>
</span>
<span class="label label-success innerWidth_log">
.target innerWidth: <span></span>
</span>
<span class="label label-success outerWidth_log">
.target outerWidth: <span></span>
</span>
</p>
<p>
<span class="label label-success windowWidth_log">
window width: <span></span>
</span>
<span class="label label-success documentWidth_log">
document width: <span></span>
</span>
</p>
</div>
<div class="target2">
<span class="label label-success width2">width:<span></span></span>
<span>width of this block set by jQuery (same as .target block)</span>
</div>
External resources loaded into this fiddle: