I'm currently trying to use

var divAWidth = $('#divA').css('width');

$('#divB').css('height', divAWidth);

If you have a look at http://wrestlingvoiceradio.com/2014 - I'm using Wordpress, but I want the height of #divB to be determined by the width of #divA, the CSS width value is 100% so it changes obviously, but I want to determine the current width and make that the height of #divB

Cheers