javascript calculate percentage to pixel
<div id="div-1" style="width: 1000px;">
<div id="div-2" style="width: 10%;"></div>
</div>
<script language="javascript">
var percents = parseInt(document.getElementById("div-2").style.width);
var parentWidth = parseInt(document.getElementById("div-1").style.width);
var pixels = parentWidth*(percents/100);
alert(pixels); // will print "100"
</script>