...height of one (any) of the frames?
<head>
...
<script language="javascript">
var frameheight = ¿?
</script>
</head>
<frameset rows="30,*,30">
<frameset cols="30,*,60,*,30">
<frame name="top1" />
<frame name="top2" />
<frame name="top3" />
<frame name="top4" />...