This resizes a div's height proportionally to the width of it

Proportional Height CSS

#myDiv {
  width: 100%;
  height: 0px; /*arbitrary number, 0 may be best to use until jquery calculation runs */
}

Proportional Height HTML

<div id="myDiv">
	<p>This is a div with some content in it</p>
</div>

Proportional Height JS

$(document).ready(function() {
  var windowWidth = $(window).width(); //grabbing window width

	$('#myDiv').css('height', windowWidth * .667); //running the initial sizing function on page load

  //rerunning the function on window resizing
	$(window).resize(function() {
		windowWidth = $(window).width();
		$('#myDiv').css('height', windowWidth * .667);
	});
  
});