.col-lg-* class is for larger screen, which is wider than 940px.
.col-sm-* class is for smaller screen, which is wider than 728px but less than 940px.
.col-* class is for extra smaller screen.
The following code uses the style for smaller screen.
<!DOCTYPE HTML>
<html>
<head>
<link href="http://java2s.com/style/bootstrap.min.css" rel="stylesheet">
<style>div{background:#eee;border:1px solid #DDD;}</style>
<!--from w ww . j ava2 s . c o m-->
</head>
<body style='margin:20px;'>
<div class="row">
<div class="col-sm-8">8</div>
<div class="col-sm-4">4</div>
</div>
</body>
</html>