autosize
by New_To_JS
HTML
<textarea id="autosize" style="width:200px;">a
b
c</textarea>
<script src="https://code.jquery.com/jquery-1.11.0.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/autosize.js/1.18.4/jquery.autosize.min.js"></script>
<script>$('#autosize').autosize()</script>