Animate element to auto height with jQuery

1. Save the current height:

   var curHeight = $('#first').height();
   

2. Temporarily switch the height to auto:

   $('#first').css('height', 'auto');
   

3. Get the auto height:

   var autoHeight = $('#first').height();
   

4. Switch back to curHeight and animate to autoHeight:

   $('#first').height(curHeight).animate({height: autoHeight}, 1000);
   

And together:

var el = $('#first'),
    curHeight = el.height(),
    autoHeight = el.css('height', 'auto').height();
el.height(curHeight).animate({height: autoHeight}, 1000);