Scale Text JS is a simple to use plugin for jQuery that allows you to scale text to the width AND height of the container component. Its really easy to set up.
<script type="text/javascript" src="http://code.jquery.com/jquery-2.1.0.min.js"></script>
<script type="text/javascript" src="scaletext.js"></script>
make sure to have the correct markup
<div class="mydiv">
<span>ScaleText JS</span>
</div>
then simply scale the text with the following selector
$(".mydiv").scaletext();