ksa,
<div class="pdf" style="width: 100px;"></div>
<div class="pdf" style="width: 200px;"></div>
<div class="pdf" style="width: 300px;"></div>
<div class="pdf" style="width: 400px;"></div>
<div class="pdf" style="width: 5px;"></div>
<script>
var o = document.getElementsByClassName('pdf');
var max=0;
for (var i = 0; i < o.length; ++i) {
var val = +o[i].style.width.replace('px', '');
if (val>max) max=val;
}
alert(max);
</script>