How to find the height of a partially hidden div?


I am creating a vertical scrolling text using jquery animate() function and I need to know the height of the partially hidden text in the div as it scrolls.

I have set the parent div to overflow hidden.

I am able to create the sequence of text to rotate from the bottom to the top.
But it doesn’t scroll smoothly as the distance to scroll is wrong.

Is there a javascript/jquery method to know how much the animate method has already partially scrolled the div that has gone hidden?