They should stretch fine to whatever the width of the container element is, or just set it. Also they should stretch fine to whatever height you give .meter.
<div class="meter">
<span style="width: 25%"></span>
</div>
<div class="meter orange nostripes">
<span style="width: 33.3%"></span>
</div>
<div class="meter red">
<span style="width: 80%"></span>
</div>
<div class="meter animate">
<span style="width: 50%"><span></span></span>
</div>