используйте эту функцию
<script>
function textAreaCounter(field,cntfield,maxlimit)
{
if (field.value.length > maxlimit)
field.value = field.value.substring(0, maxlimit);
else cntfield.value = maxlimit - field.value.length;
}
</script>
<form name="frmlist" id="frmlist" method="post">
<div>
<textarea rows="8" cols="70" name="description" id="description" onFocus="textAreaCounter(document.frmlist.description,document.frmlist.descriptionCount,1000)" onKeyDown="textAreaCounter(document.frmlist.description,document.frmlist.descriptionCount,1000)" onKeyUp="textAreaCounter(document.frmlist.description,document.frmlist.descriptionCount,1000)"></textarea>
<br>
<br>
<em>Characters remaining:</em>
<input type="text" name="descriptionCount" id="descriptionCount" readonly="" size="5" value="<?php if(isset($frmdata['descriptionCount'])){echo $frmdata['descriptionCount']; } else{ echo '1000'; }?>" >
</div></form>