I just wrote a script that returns a div's height compared to it's parent into percentage.
I just need to find a way to display that height change in real time while animating the change.
This is what I have so far: jsFiddle
JS:
var full = $('#wrap').height();
var value = $('#bla').height();
var percentage = value*100/full ;
$('h1').html( percentage + '%');
$('#bla').delay(1500).animate({
height: '74%'
},2200, "easeOutElastic");
see this fiddle
you can set an interval which looks for the height of the div and update the text accordingly
var inter=setInterval(function(){
var full = $('#wrap').height();
var value = $('#bla').height();
var percentage = value*100/full ;
$('h1').html( percentage + '%');
},10)