No te entiendo... funciona bien de las 2 maneras, aunque es 16.6%:
Código HTML:
<table width="100%" border="1">
<tr>
<td width="16.6%" align="right" id="linea">4</td>
<td width="16.6%" align="right" id="linea">4</td>
<td width="16.6%" align="right" id="linea">4</td>
<td width="16.6%" align="right" id="linea">4</td>
<td width="16.6%" align="right" id="linea">4</td>
<td width="16.6%" align="right" id="linea">4</td>
</tr>
</table>