fast/forms/textarea-scroll-height.html

<textarea id="area" style="width:200px;height:200px">
Lots of content.
Lots of content.
Lots of content.
Lots of content.

Lots of content.
Lots of content.

Lots of content.
Lots of content.

Lots of content.
Lots of content.

Lots of content.
Lots of content.

Lots of content.
Lots of content.

Lots of content.
Lots of content.

</textarea>
<script>
document.write(document.getElementById('area').scrollWidth + " " + document.getElementById('area').scrollHeight);
</script>