Size calculator

<form name="calculator">
<table width="365" cellpadding="5">
<tbody>
<tr>
<td align="right">length:</td>
<td><input type="text" name="length" size="4" /> inches</td>
<td width="180" align="center" style="font-size: 16px;" rowspan="3">SQUARE FEET: <input type="text" style="border: 0pt none ; background-color: white; color: black;font-weight:bold;" disabled="" value="0" name="squarefeet" size="4" /></td>
</tr>
<tr>
<td align="right">width:</td>
<td><input type="text" name="width" size="4" /> inches</td>
</tr>
<tr>
<td></td>
<td><input type="button" onclick="calculator.squarefeet.value=Math.ceil((calculator.length.value * calculator.width.value)/144);" value="calculate" /></td>
</tr>
</tbody>
</table>
</form>