The symbolwidth is a numeric value, which determines the width for a single star or symbol for the rating control.
This is important if changing the default symbol.
The default value is 16.

The code below demonstrates one such use:

<div id="rating"></div>

<script type="text/javascript">
jQuery(function($) {
        step: 1,
        value: 3,
        markPreset: false,
        symbolWidth: 20

Please, keep in mind that this will change only the spacing for the star/symbol used by the rating.
You will also need to change the symbol image from the base control css file, in order to completely change the dimension.