Edit in JSFiddle

var logging = false,
				l = function( log ){if (logging == true){console.log(log)}};

			function textResize( elem ) {
				var child = $( elem ).children(),
					parent = $( elem ),
					runs;

				//Setup the enlarge and contract functions to be used later on if needed
				function enlarge() {
					if (child.height() < parent.height()) {
						child.css("font-size", parseInt(child.css("font-size").replace("px",""))+1+"px");

						l("enlarging child");

						enlarge();
					} else if (child.height() > parent.height()) {
						contract();
					}
				};
				function contract() {
					if (child.height() > parent.height()) {
						child.css("font-size", parseInt(child.css("font-size").replace("px",""))-1+"px");

						l("contracting child");

						contract();
					} 
				};

				//decide if we need to enlarge or contract the child element
				if (runs === undefined) {
					if(child.height() < parent.height()) {
						//Enlarge
						enlarge();
					} else if (child.height() > parent.height()) {
						//Contract
						contract();
					}
				}
			}

			textResize("#container");
			
			$( window ).resize(function(){
				textResize("#container");
			});

<div id="container">
			<p>This is some text that will be large and need to be shrunken down to be usable here</p>
		</div>

		<div id="output"></div>

* {
				padding: 0;
				margin: 0;
			}
			body {
				font-size: 46px;
				font-family: Helvetica, Arial, Sans-Serif;
			}
			div {
				width: 80%;
				margin: 0 auto;
			}
			#container {
				background: #fff;
				color: #333;
				padding: 20px;
				height: 130px;
			}
			#container p {
				/*transition: font-size 0.1s ease;*/
			}
			#output {
				font-family: serif;
				font-size: 18px;
			}