How to automatically change the text size inside a div?

I understand your question this way, you would like to fit some text into a given div with a fixed dimension, and if the div is too small to show all the text, the font size should be shrinked until the text fits into the div. If that’s the point, here is my solution.

Here is an example with a jQuery implementaion: http://jsfiddle.net/MYSVL/2/

Here is a div

<div id="fitin">
    <div>Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.</div>
</div>

With a fixed size

#fitin {
    width: 300px;
    height: 100px;
    border: 1px solid black;
    overflow: hidden;
    font-size: 1em;
}

This JavaScript will do the job.

$(function() {
    while( $('#fitin div').height() > $('#fitin').height() ) {
        $('#fitin div').css('font-size', (parseInt($('#fitin div').css('font-size')) - 1) + "px" );
    }
});