<script type="text/javascript">
$(document).ready(function(){
   var height = $("#main").height();
	if (height > 700) {
	  $(".top").show();
	 } else {
	  $(".top").hide();
	}
});
</script>
 
<div id="main" style="border:1px dashed #ccc;">
    <p>If content in this div gets higher than 700px, link will show</p>
</div>
<div class="top"><a href="#">Back to top</a></div>

http://www.vagrantradio.com/demos/top_link/index.html

JQUERY DISPLAY BACK TO TOP LINK BASED ON PAGE HEIGHT

resize, link, jquery, body

jQuery